| 1. |
- Steinbach, C, et al.
(författare)
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Detection of the Book Isomer from the OH-stretch Spectroscopy of Size Selected Water Hexamers.
- 2004
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Ingår i: Physical Chemistry Chemical Physics. ; 6, s. 3320-3324
-
Tidskriftsartikel (refereegranskat)abstract
- The vibrational OH-stretch spectrum of size selected water hexamer clusters has been measured for cluster temperatures between 40 and 60 K. By comparison with temperature dependent calculations the spectra were identified to be those of the book isomer. This result is in good agreement with recent predictions of the equilibrium isomer distributions in this temperature range.
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| 2. |
- Steinbach, C, et al.
(författare)
-
Infrared Predissociation Spectroscopy of Large Water Clusters: a Unique Probe of Cluster Surfaces.
- 2004
-
Ingår i: J. Physical Chemistry A. ; 108, s. 6165-6174
-
Tidskriftsartikel (refereegranskat)abstract
- The vibrational OH-stretch spectra of large water clusters were measured by photofragment spectroscopy after the absorption of pulsed tunable infrared radiation in the frequency range from 3000 to 3800 cm-1. The mean size of the clusters from = 20 to 1960 was measured by threshold photoionization of the water clusters doped with sodium atoms. The largest abundance of the fragments was that of water hexamers. The fragment intensities are measured for different excitation energies and different cluster temperatures as function of the cluster size. For the selected sizes = 48, 111, 631, and 1960 complete OH-stretch spectra have been measured. The comparison with calculations revealed that the method is mainly sensitive to the outer cluster surface which has for all sizes an amorphous structure dominated by 3-coordinated and to a lesser extent also by 4-coordinated molecules. The intensity of the hexamer fragments goes through a maximum at n = 70 and drops to n = 300 where it levels off with a different slope. This behavior is attributed to the number of available connected 3-coordinated water molecules and the influence of the emerging 4-coordinated molecules in these clusters.
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| 3. |
- Al-Khalili, A, et al.
(författare)
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Dissociative recombination cross section and branching ratios of protonated dimethyl disulfide and N-methylacetamide
- 2004
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:12, s. 5700-5708
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Tidskriftsartikel (refereegranskat)abstract
- Dimethyl disulfide (DMDS) and N-methylacetamide are two first choice model systems that represent the disulfide bridge bonding and the peptide bonding in proteins. These molecules are therefore suitable for investigation of the mechanisms involved when proteins fragment under electron capture dissociation (ECD). The dissociative recombination cross sections for both protonated DMDS and protonated N-methylacetamide were determined at electron energies ranging from 0.001 to 0.3 eV. Also, the branching ratios at 0 eV center-of-mass collision energy were determined. The present results give support for the indirect mechanism of ECD, where free hydrogen atoms produced in the initial fragmentation step induce further decomposition. We suggest that both indirect and direct dissociations play a role in ECD.
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| 4. |
- Andersson, Patrik U, 1970, et al.
(författare)
-
Carbon dioxide interactions with crystalline and amorphous ice surfaces
- 2004
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 108:21, s. 4627-4631
-
Tidskriftsartikel (refereegranskat)abstract
- Carbon dioxide interactions with crystalline and amorphous water ice have been studied by time-resolved molecular beam techniques. CO2 collisions at thermal kinetic energies with ice in the temperature range 100-160 K result in efficient trapping on the ice surface followed by desorption. The desorption kinetics on crystalline ice at 100-125 K are well described by the Arrhenius equation with an activation energy of 0.22 +/- 0.02 eV and a preexponential factor of 10(13.32+/-0.57) s(-1). Below 120 K, CO2 populates strongly bonded sites on amorphous ice, resulting in surface residence times on the order of minutes at 100 K, and the desorption data can in this case not be explained by a simple first-order process. The results are compared to previous studies of gas-ice interactions, and the implications for heterogeneous processes in the terrestrial atmosphere are discussed.
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| 5. |
- Andersson, Patrik U, 1970, et al.
(författare)
-
Cluster ions DN + ejected from dense and ultra-dense deuterium by Coulomb explosions: Fragment rotation and D+ backscattering from ultra-dense clusters in the surface phase
- 2012
-
Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806. ; 310, s. 32-43
-
Tidskriftsartikel (refereegranskat)abstract
- The two forms of condensed atomic deuterium, dense deuterium D(1) and ultra-dense deuterium D(−1), can be studied by laser-induced Coulomb explosion time-of-flight mass spectrometry and neutral timeof- flight. In the present study pulsed laser intensity below 1014W cm−2 is used. Cluster ions DN + from D(1) are observed with N = 3, 4, 12 and 17, thus not in close-packed forms. Clusters DN(1) are mainly in the form of chains of D2 and D3 groups, a shape derived from the D(−1) material which D(1) is spontaneously converted to. Only atomic ions D+ with initial kinetic energy of hundreds of eV are observed from D(−1). Half of these ions are ejected from the emitter surface, half of them penetrate into the ultra-dense D(−1) layer on the emitter surface. This second half of the ions is reflected completely from the surface layer formed by ultra-dense D(−1) strongly bonded clusters D3(−1) and D4(−1).
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| 6. |
- Andersson, Patrik U, 1970, et al.
(författare)
-
Deuteron energy of 15 MK in ultra-dense deuterium without plasma formation: Temperature of the interior of the Sun
- 2010
-
Ingår i: Physics Letters A. - 0375-9601. ; 374:28, s. 2856-2860
-
Tidskriftsartikel (refereegranskat)abstract
- Deuterons are released with kinetic energy up to 630 eV from ultra-dense deuterium as shown previously, by Coulomb explosions initiated by ns laser pulses at < 1011 Wcm−2. With higher laser intensity at < 1014 Wcm−2, the initial kinetic energy now observed by TOF-MS with variable acceleration energy is up to 1100 eV per deuteron. This indicates ejection of one deuteron by Coulomb repulsion from two stationary charges in the material. It proves a full kinetic energy release of 1260 eV or a deuteron temperature of 15 MK, similar to the temperature in the interior of the Sun. Plasma processes are excluded by the sharp TOF peaks observed and by the slow signal variation with laser intensity. Deuterons with even higher energy from multiple charge repulsion are probably detected. D + D fusion processes are expected to exist in the ultra-dense phase without plasma formation.
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| 7. |
- Andersson, Patrik U, 1970, et al.
(författare)
-
Efficient source for the production of ultradense deuterium D(-1) for laser-induced fusion (ICF)
- 2011
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 82
-
Tidskriftsartikel (refereegranskat)abstract
- A novel source which simplifies the study of ultradense deuterium D(-1) is now described. This means one step further toward deuterium fusion energy production. The source uses internal gas feed and D(-1) can now be studied without time-of-flight spectral overlap from the related dense phase D(1). The main aim here is to understand the material production parameters, and thus a relatively weak laser with focused intensity ≤1012 W cm−2 is employed for analyzing the D(-1) material. The properties of the D(-1) material at the source are studied as a function of laser focus position outside the emitter, deuterium gas feed, laser pulse repetition frequency and laser power, and temperature of the source. These parameters influence the D(-1) cluster size, the ionization mode, and the laser fragmentation patterns.
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| 8. |
- Andersson, Patrik U, 1970, et al.
(författare)
-
Fast atoms and negative chain-cluster fragments from laser-induced Coulomb explosions in a super-fluid film of ultra-dense deuterium D(-1)
- 2012
-
Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 86:4
-
Tidskriftsartikel (refereegranskat)abstract
- Fragments from laser-induced Coulomb explosions (CE) in a thin super-fluid film of ultra-dense deuterium D(-1) on a vertical surface are now observed by both negative and positive time-of-flight mass spectrometry. The so-called normal phase of the super-fluid is probably associated with D-4 clusters and gives only neutral atomic fragments with a kinetic energy from the CE of 945 eV. The super-fluid phase is associated with long chain clusters D-2N with N deuteron pairs and gives cluster fragments by CE mainly with a kinetic energy of 315 eV from the central cleavage in a neutral, positive or negative form. This indicates that the chain clusters are standing perpendicularly to the surface. The fragment charge state is influenced by the external field, which indicates efficient charge transfer processes.
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| 9. |
- Andersson, Patrik U, 1970, et al.
(författare)
-
Formation of Highly Rovibrationally Excited Ammonia from Dissociative Recombination of NH4
- 2010
-
Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 1:17, s. 2519-2523
-
Tidskriftsartikel (refereegranskat)abstract
- The internal energy distribution of ammonia formed in the dissociative recombination (DR) of NH4+ with electrons has been studied by an imaging technique at the ion storage ring CRYRING. The DR process resulted in the formation of NH3 + H (0.90 ± 0.01), with minor contributions from channels producing NH2 + H2 (0.05 ± 0.01) and NH2 + 2H (0.04 ± 0.02). The formed NH3 molecules were highly internally excited, with a mean rovibrational energy of 3.3 ± 0.4 eV, which corresponds to 70% of the energy released in the neutralization process. The internal energy distribution was semiquantitatively reproduced by ab initio direct dynamics simulations, and the calculations suggested that the NH3 molecules are highly vibrationally excited while rotational excitation is limited. The high internal excitation and the translational energy of NH3 and H will influence their subsequent reactivity, an aspect that should be taken into account when developing detailed models of the interstellar medium and ammonia-containing plasmas.
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| 10. |
- Andersson, Patrik U, 1970, et al.
(författare)
-
Fusion Generated Fast Particles by Laser Impact on Ultra-Dense Deuterium: Rapid Variation with Laser Intensity
- 2012
-
Ingår i: Journal of Fusion Energy. - : Springer Science and Business Media LLC. - 0164-0313 .- 1572-9591. ; 31, s. 249-256
-
Tidskriftsartikel (refereegranskat)abstract
- Nuclear fusion D+D processes are studied by nanosecond pulsed laser interaction with ultra-dense deuterium. This material has a density of 1029 cm-3 as shown in several previous publications. Laser power is \2 W (0.2 J pulses) and laser intensity is\1014 W cm-2 in the 5–10 lm wide beam waist. Particle detection by time-offlight energy analysis with plastic scintillators is used. Metal foils in the particle flux to the detector remove slow ions, and make it possible to convert and count particles with energy well above 1 MeV. The variation of the signal of MeV particles from D?D fusion is measured as a function of laser power. At relatively weak laser-emitter interaction, the particle signal from the laser focus varies as the square of the laser power. This indicates collisions in the ultra-dense deuterium of two fast deuterons released by Coulomb explosions. During experiments with stronger laser-emitter interaction, the signal varies approximately as the sixth power of the laser power, indicating a plasma process. At least 2 9 106 particles are created by each laser pulse at the maximum intensity used. Our results indicate break-even in fusion at a laser pulse energy of 1 J with the same focusing, in approximate agreement with theoretical results for ignition conditions in ultra-dense deuterium. Radiation loss at high temperature will however require higher laser energy at break-even.
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| 11. |
- Andersson, Patrik U, 1970, et al.
(författare)
-
Isotope exchange and structural rearrangements in reactions between size-selected ionic water clusters, H3O+(H2O)n and NH4+(H2O)n, and D2O
- 2008
-
Ingår i: Phys.Chem.Chem.Phys. - : Royal Society of Chemistry (RSC). ; 10, s. 6127-6134
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrogen/deuterium exchange in reactions of H3O+(H2O)n and NH4+(H2O)n (1 n 30) with D2O has been studied experimentally at center-of-mass collisions energies of 0.2 eV. For a given cluster size, the cross-sections for H3O+(H2O)n and NH4+(H2O)n are similar, indicating a structural resemblance and energetics of binding. For protonated pure water clusters, H3O+(H2O)n, reacting with D2O the main H/D exchange mechanism is found to be proton catalyzed. In addition the H/D scrambling becomes close to statistically randomized for the larger clusters. For NH4+(H2O)n clusters reacting with D2O, the main mechanism is a D2O/H2O swap reaction. The lifetimes of H3O+(H2O)n clusters have been estimated using RRKM theory and a plateau in lifetime vs. cluster size is found already at n = 10.
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| 12. |
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| 13. |
- Andersson, Patrik U, 1970, et al.
(författare)
-
Search for Superconductivity in Ultra-dense Deuterium D(-1) at Room Temperature: Depletion of D(-1) at Field Strength > 0.05 T
- 2012
-
Ingår i: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1939 .- 1557-1947. ; 25:4, s. 873-882
-
Tidskriftsartikel (refereegranskat)abstract
- Ultra-dense deuterium D(-1) is expected to be both a superfluid and a superconductor as shown by recent theoretical research. Condensed D(-1) can be deposited on surfaces by a source which produces a stream of clusters. A magnetic field strongly influences the type of material formed. Very little of D(-1) and of the form D(1), which is strongly coupled to D(-1), exists on the magnet surface or within several mm from the magnet surface. Even the formation of D(-1) on the source emitter is strongly influenced by a magnetic field, with a critical field strength in the range 0.03-0.07 T. Higher excitation levels D(2) and D(3) dominate in a magnetic field. The excitation level D(2) is now observed for the first time. The removal of D(-1) and D(1) in strong magnetic fields is proposed to be due to a Meissner effect in long D(-1) clusters by large-orbit electron motion. The lifting of long D(-1) clusters above the magnet surface is slightly larger than expected, possibly due to the coupling to D(1). The previously reported oscillation between D(-1) and D(1) in an electric field is proposed to be due to destruction of D(-1).
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| 14. |
- Andersson, Patrik U, 1970, et al.
(författare)
-
Superfluid ultra-dense deuterium D(-1) at room temperature
- 2011
-
Ingår i: Physics Letters A. - : Elsevier BV. - 0375-9601. ; 375, s. 1344-1347
-
Tidskriftsartikel (refereegranskat)abstract
- Ultra-dense deuterium D(−1) is expected to be both superfluid and superconductive. It is deposited on surfaces below a novel source producing a stream of D(−1) clusters. It is studied by laser probing and Coulomb explosions giving cluster fragments which are observed by time-of-flight measurements. It is observed on surfaces at a few cm height above the container below the source, and on the outside of the container. D(−1) is detected above a 1 cm long vertical capillary in vacuum (fountain effect). This suggests the existence of superfluid D(−1) which is the only material that may be superfluid at room temperature.
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| 15. |
- Andersson, Patrik U, 1970, et al.
(författare)
-
Ultra-dense deuterium: A possible nuclear fuel for inertial confinement fusion (ICF)
- 2009
-
Ingår i: Physics Letters A. ; 373, s. 3067-3070
-
Tidskriftsartikel (refereegranskat)abstract
- The ejection of deuterons with kinetic energy release (KER) of 630 eV was proved recently by measuring the laser-induced ion time-of-flight (TOF-MS) with two different detectors at different distances [S. Badiei, P.U. Andersson, L. Holmlid, Int. J. Mass Spectrom. 282 (2009) 70]. Realizing that the only possible energy release mechanism is Coulomb explosions, the D–D distance in the ultra-dense deuterium was determined to be constant at 2.3 pm. Using a long TOF-MS path now gives improved resolution. We show the strong effect of collisions in the ultra-dense material, and demonstrate that the kinetic energy of the ions increases with laser pulse power but that the number of ions formed is independent of the laser pulse power. This indicates special properties of the material. We also show that the two forms of condensed deuterium D(1) and D(−1) can be observed simultaneously as well resolved mass spectra of different forms. No intermediate bond lengths are observed. The two forms of deuterium are stable and well separated in bond length. We suggest that they switch rapidly back and forth as predicted by theory. A loosely built form with planar clusters of D(1) is observed here to be related to D(−1) formation.
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| 16. |
- Andersson, Patrik U, 1970, et al.
(författare)
-
Water Condensation on Graphite Studied by Elastic Helium Scattering and Molecular Dynamics Simulations
- 2007
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:42, s. 15258-15266
-
Tidskriftsartikel (refereegranskat)abstract
- Formation of water/ice layers on graphite has been studied in the temperature range from 90 to 180 K by elastic helium scattering, light scattering, and molecular dynamics simulations. Combined helium- and light-scattering experiments show that an ice film that wets the graphite surface is formed at surface temperatures of 100-140 K, whereas three-dimensional ice structures are formed at 140-180 K. Desorption of adsorbed water molecules competes with water incorporation into the ice film, and the ice formation rate is strongly temperature dependent. At 150 K, ice-layer formation takes place at the same time scale as layer reconstruction, and its properties are sensitive to the water deposition rate. The experimental results are compared with kinetics models, and the Johnston-Mehl-Avrami-Kolmogorov model is concluded to well describe the ice-layer formation kinetics in the whole temperature range. Molecular dynamics simulations of water-cluster formation on graphite at 90-180 K show that water molecules and small clusters are highly mobile on the surface, which rapidly results in the nucleation of large and less mobile clusters on the surface. Clusters formed at low temperature tend to have the most molecules in direct contact with the uppermost graphite layer, while multilayer cluster structures are preferred at high temperatures. The results are discussed and compared with earlier studies of water ice formation on solid surfaces.
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| 17. |
- Badiei, Shahriar, 1969, et al.
(författare)
-
Fusion reactions in high-density hydrogen: A fast route to small-scale fusion?
- 2009
-
Ingår i: International Journal of Hydrogen Energy. ; 34, s. 487-495
-
Tidskriftsartikel (refereegranskat)abstract
- High-density atomic hydrogen, which is believed to be a quantum liquid, can be formed by heterogeneous catalysis at the surface of hydrogen-transfer metal oxide catalysts. Extensive studies have been made of the hydrogen phase named H(1), with interatomic distance of 150 pm found by Coulomb explosion measurements. This bond distance corresponds to a material density of 0.5–0.7 kgdm-3. The use of this material as fusion target for inertial confinement fusion (ICF) is proposed in J Fusion Energy 2008;27:296–300. A much denser hydrogen (deuterium) material D(-1) also exists with an interatomic distance of 2.3 pm. This material is probably the inverse of metallic D(1), where nuclei and electrons exchange their roles. The ICF process would be greatly simplified if the intended initial multi-laser compression stage was not necessary. The close-packed density of D(-1) is calculated from the bond distance as >130 kg cm-3. This is much higher than that required for ‘‘fast ignition’’ laser-driven fusion (>0.3 kg cm-3). It may mean that a method already exists to prepare dense hydrogen fuel for small-scale laser-driven fusion. The high energy particles observed experimentally (up to 150 keV/atomic mass unit in the peak or 10^9 K) indicate that high energy processes exist at relatively low laser intensities.
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| 18. |
- Badiei, Shahriar, 1969, et al.
(författare)
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High-energy Coulomb explosions in ultra-dense deuterium: Time-of-flight-mass spectrometry with variable energy and flight length
- 2009
-
Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806. ; 282, s. 70-76
-
Tidskriftsartikel (refereegranskat)abstract
- High-density hydrogen is of great interest both as a fuel with the highest energy content of any combustion fuel, and as a target material for laser initiated inertial confinement fusion (ICF) [S. Badiei, L. Holmlid, J. Fusion Energ. 27 (2008) 296]. A much denser deuterium material named D(−1) can be observed by pulsed laser induced Coulomb explosions giving a well-defined, high kinetic energy release (KER). Neutral time-of-flight of the fragments from the material shows that the Coulomb explosions have a KER of 630 eV [S. Badiei, P.U. Andersson, L. Holmlid, Int. J. Hydrogen Energ. 34 (2009) 487]. By using ion time-of-flight-mass spectrometry (TOF-MS) with variable acceleration voltages and a few different values of laser pulse power, we now prove the mass and charge of the particles as well as the KER. In fact, the ions are so fast that they must be H+, D+ or T+. By using two different flight lengths, we prove with certainty that the spectra are due to D+ ions and not to photons or electromagnetic effects. The results also establish the fragmentation patterns of the ultra-dense D(−1) material in the electric field. The energy release of 630 ± 30 eV corresponds to an interatomic distance D–D of 2.3 ± 0.1 pm. This material is probably an inverted metal with the deuterons moving in the field from the stationary electrons, which gives a predicted interatomic distance of 2.5 pm, close to the measured value. Thus, we prove that an ultra-dense deuterium material exists.
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| 19. |
- Badiei, Shahriar, 1969, et al.
(författare)
-
Laser-driven nuclear fusion D+D in ultra-dense deuterium: MeV particles formed without ignition
- 2010
-
Ingår i: Laser and Particle Beams. - 0263-0346. ; 28:2, s. 313-317
-
Tidskriftsartikel (refereegranskat)abstract
- The short D-D distance of 2.3 pm in the condensed material ultra-dense deuterium means that it is possible that only a small disturbance is required to give D+D fusion. This disturbance could be an intense laser pulse. The high excess kinetic energy of several hundred eV given to the deuterons by laser induced Coulomb explosions in the material increases the probability of spontaneous fusion without the need for a high plasma temperature. The temperature calculated from the normal kinetic energy of the deuterons of 630 eV from the Coulomb explosions is 7 MK, maybe a factor of 10 lower than required for ignition. We now report on experiments where several types of high-energy particles from laser impact on ultra-dense deuterium are detected by plastic scintillators. Fast particles with energy up to 2 MeV are detected at a time-of-flight as short as 60 ns, while neutrons are detected at 50 ns time-of-flight after passage through a steel plate. A strong signal peaking at 22.6 keV u-1 is interpreted as due to mainly T retarded by collisions with H atoms in the surrounding cloud of dense atomic hydrogen.
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| 20. |
- Badiei, Shahriar, 1969, et al.
(författare)
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Laser-induced variable pulse-power TOF-MS and neutral time-of-flight studies of ultradense deuterium
- 2010
-
Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 81:4, s. 045601 1-13
-
Tidskriftsartikel (refereegranskat)abstract
- The ultradense atomic deuterium material named D(−1) is conveniently studied by laser-induced Coulomb explosion methods. A well-defined high kinetic energy release (KER) from this material was first reported in Badiei et al (2009 Int. J. Hydrog. Energy 34 487) and a two-detector setup was used to prove the high KER and the complex fragmentation patterns in Badiei et al (2009 Int. J. Mass Spectrom. 282 70). The common KER is 630±30 eV, which corresponds to an interatomic distance D–D of 2.3±0.1 pm. In both ion and neutral time-of-flight (TOF) measurement, two similar detectors at widely different flight distances prove that atomic particles are observed. New results on neutral TOF spectra are now reported for the material D(−1). It is shown that density changes of D(−1) are coupled to similar changes in ordinary dense D(1), and it is proposed that these two forms of dense deuterium are rapidly transformed into each other. The TOF-MS signal dependence on the intensity of the laser is studied in detail. The fast deuteron intensity is independent of the laser power over a large range, which suggests that D(−1) is a superfluid with long-range efficient transport of excitation energy or particles.
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| 21. |
- Badiei, Shahriar, 1969, et al.
(författare)
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Production of ultradense deuterium: A compact future fusion fuel
- 2010
-
Ingår i: Applied Physics Letters. - 1077-3118. ; 96:12
-
Tidskriftsartikel (refereegranskat)abstract
- Ultradense deuterium as a nuclear fuel in laser-ignited inertial confinement fusion appears to have many advantages. The density of ultradense deuterium D(−1) is as high as 140 kg cm−3 or 10^29 cm−3. This means that D(−1) will be very useful as a target fuel, circumventing the complex and unstable laser compression stage. We show that the material is stable apart from the oscillation between two forms, and can exist for days in the laboratory environment. We also demonstrate that an amount of D(−1) corresponding to tens of kilojoules is produced in each experiment. This may be sufficient for break-even.
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| 22. |
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| 23. |
- Hansen, Klavs, 1958, et al.
(författare)
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Activation energies for evaporation from protonated and deprotonated water clusters from mass spectra
- 2009
-
Ingår i: journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental mass abundance spectra are used to extract evaporative activation energies (dissociation energies) for protonated water clusters, (H$_2$O)$_N$H$^+$, and deprotonated water clusters, (H$_2$O)$_N$ OH$^-$, in the size range up to hundred molecules. The inversion is achieved by application of the shell correction method adapted from nuclear physics to the abundance spectra. The well known abundance anomaly for protonated clusters which occurs for $N = 20-22$ is found to have the characteristic behavior of a shell closing, whereas other apparent magic numbers are only prominent peaks in the abundance spectra because of the instability of the evaporative precursor. For the deprotonated clusters, we find a similar shell closing for $N = 55-56$.
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| 24. |
- Janhäll, Sara, 1965, et al.
(författare)
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Evolution of the urban aerosol during winter temperature inversion episodes
- 2006
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 40:28, s. 5355-5366
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Tidskriftsartikel (refereegranskat)abstract
- Winter temperature inversions are for Nordic urban sites a major cause for exceeding air-quality legislation thresholds for most primary pollutants. In this study, number particle size distributions have been measured and compared to other tracers for traffic emissions. Concentrations during winter days with and without morning temperature inversion were compared. Morning temperature inversion resulted in high concentrations of traffic-related pollutants, including CO, NO and NO2 together with ultrafine particles, while the pollution levels where considerably lower during mornings without temperature inversion. The specific time trends of NOx species could be well understood when considering the reaction with O-3. The two different particle measures used in this study, i.e. the number concentration of ultrafine particles (10-100 nm) and the mass of particles below 10 pm (PM10), both increased during morning rush hours. When the morning inversion broke up and ground-level air mixed with air aloft, the number of particles decreased more rapidly than PM10 concentrations. LIDAR measurements were used to follow the vertical distribution of particles, and they clearly showed how the mixing processes started after the morning inversion and resulted in rising of the inversion followed by a relatively well-mixed boundary layer with a height of I kin around 14:00. (c) 2006 Elsevier Ltd. All rights reserved.
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| 25. |
- Kong, Xiangrui, et al.
(författare)
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Environmental molecular beam studies of ice surface processes
- 2011
-
Ingår i: Physics and Chemistry of Ice 2010 (The 12th International Conference on the Physics and Chemistry of Ice, Sapporo, Japan, September 5-10, 2010, Eds. Y. Furukawa, G. Sazaki, T. Uchida, N. Watanabe, Hokkaido University Press, Sapporo, Japan, 2011). - 9784832903616 ; , s. 79-88
-
Konferensbidrag (refereegranskat)abstract
- The development and application of a new molecular beam setup for studies of gas-ice interactions at pressures in the 0.001 mbar range is described. Direct simulation Monte Carlo calculations have been applied to optimize the experimental design with respect to gas transmission through the high pressure zone outside the ice surface and pressure along the surface plane. In a first application of the new setup elastic helium scattering and light scattering have been used to study the formation of water, methanol and water-methanol ice on a graphite surface in the temperature range from 180 to 215 K. Water does not wet the graphite surface under these conditions, in agreement with earlier results obtained below 180 K, while methanol readily forms a thin layer on the surface. Methanol enhances water ice nucleation and influences the properties of the ice formed, but does not have a major impact on ice growth or evaporation once a thick water-containing ice layer has formed. The potential for further development of the molecular beam technique are discussed.
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| 26. |
- Kong, Xiangrui, et al.
(författare)
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Ice Formation via Deposition Mode Nucleation on Bare and Alcohol-Covered Graphite Surfaces
- 2012
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:16, s. 8964-8974
-
Tidskriftsartikel (refereegranskat)abstract
- Deposition of water on aerosol particles contributes to ice cloud formation in the atmosphere with implications for the water cycle and climate on Earth. The heterogeneous ice nucleation process is influenced by physicochemical properties of the substrate, but the mechanisms remain incompletely understood. Here, we report on ice formation on bare and alcohol-covered graphite at temperatures from 175 to 213 K, probed by elastic helium and light scattering. Water has a low wettability on bare and butanol-covered graphite resulting in the growth of rough ice surfaces. In contrast, preadsorbed methanol provides hydrophilic surface sites and results in the formation of smooth crystalline ice; an effect that is pronounced also for submonolayer methanol coverages. The alcohols primarily reside at the ice surface and at the ice–graphite interface with a minor fraction being incorporated into the growing ice structures. Methanol has no observable effect on gas/solid water vapor exchange, whereas butanol acts as a transport barrier for water resulting in a reduction in ice evaporation rate at 185 K. Implications for the description of deposition mode freezing are discussed.
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| 27. |
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| 28. |
- Olofson, K. Frans G., 1976, et al.
(författare)
-
Rydberg Matter clusters of alkali metal atoms: the link between meteoritic matter, polar mesosphere summer echoes (PMSE), sporadic sodium layers, polar mesospheric clouds (PMCs, NLCs), and ion chemistry in the mesosphere
- 2010
-
Ingår i: arXiv:1002.1570v1[astro-ph.EP].
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- There exists a material which links together the influx of meteoritic matter from interplanetary space, the polar mesosphere summer echoes (PMSE), the sporadic sodium layers, the polar mesospheric clouds (PMCs, NLCs), and the observed ion chemistry in the mesosphere. The evidence in these research fields is here analyzed and found to agree well with the properties of Rydberg Matter (RM). This material has been studied with numerous methods in the laboratory. Alkali atoms, mainly Na, reach the mesosphere in the form of interplanetary (meteoritic, cometary) dust. The planar RM clusters NaN usually contain N = 19, 37 or 61 atoms, and have the density of air at 90 km altitude where they float. The diameters of the clusters are 10-100 nm from laboratory high precision radio frequency spectroscopic studies. Such experiments show that RM clusters interact strongly with radar frequencies: this explains the radio frequency heating and reflection studies of PMSE layers. The clusters give circular polarized scattering and depolarized scattering of visible light in laboratory experiments: similar effects are observed in light scattering and lidar studies of NLCs. The clusters give the low temperature in the mesosphere by efficient selective radiation at long wavelengths, which is observed in RF emission experiments. The lowest possible stable temperature of the mesopause is calculated for the first time to be 121 K in agreement with measurements, based on the strong optical activity at long wavelengths in RM. Sporadic sodium layers are explained in a unique way as due to shockwaves in the RM layers. Due to the high electronic excitation energy in RM clusters, they induce efficient reactions forming ions of all atoms and molecules in the atmosphere thus providing condensation nuclei for water vapour. This finally gives the visible part of the PMC structure. Especially the sporadic sodium layers and the PMSE give direct evidence for the existence of RM layers at the mesopause. The present contribution fills the gap between and partially replaces the separate theories used to describe the various aspects of these intriguing phenomena.
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| 29. |
- Olofson, K. Frans G., 1976, et al.
(författare)
-
Urban aerosol evolution and particle formation during wintertime temperature inversions
- 2009
-
Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 43, s. 340-346
-
Tidskriftsartikel (refereegranskat)abstract
- Aerosol temporal and spatial distributions during wintertime temperature inversions in Gothenburg, Sweden, have been characterized by ground-based and airborne particle measurements combined with lidar measurements. Ground inversions frequently developed during evenings and nights with stable cold conditions, and the low wintertime insolation often resulted in near neutral boundary layer conditions during day-time. Under these conditions ground level aerosol concentrations peaked during morning rush hours and often remained relatively high throughout the day due to inefficient ventilation. The particle number concentrations decreased slowly with increasing altitude within the boundary layer, and measurements slightly above the boundary layer suggested limited entrainment of polluted air into the free troposphere. High concentrations of ultrafine particles were observed throughout the boundary layer up to altitudes of 1100 m, which suggested that nucleation took place within the residual layer during the night and early morning. Recently formed particles were also observed around midday when the layer near ground was ventilated by mixing into the boundary layer, which indicated that ultrafine particles were either transported down from the residual layer to ground level or formed when the polluted surface layer mixed with the cleaner air above.
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| 30. |
- Petrignani, Annemieke, et al.
(författare)
-
Dissociative recombination of the weakly bound NO-dimer cation: cross sections and three-body dynamics.
- 2005
-
Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:19
-
Tidskriftsartikel (refereegranskat)abstract
- Dissociative recombination (DR) of the dimer ion (NO)(2) (+) has been studied at the heavy-ion storage ring CRYRING at the Manne Siegbahn Laboratory, Stockholm. The experiments were aimed at determining details on the strongly enhanced thermal rate coefficient for the dimer, interpreting the dissociation dynamics of the dimer ion, and studying the degree of similarity to the behavior in the monomer. The DR rate reveals that the very large efficiency of the dimer rate with respect to the monomer is limited to electron energies below 0.2 eV. The fragmentation products reveal that the breakup into the three-body channel NO+O+N dominates with a probability of 0.69+/-0.02. The second most important channel yields NO+NO fragments with a probability of 0.23+/-0.03. Furthermore, the dominant three-body breakup yields electronic and vibrational ground-state products, NO(upsilon=0)+N((4)S)+O((3)P), in about 45% of the cases. The internal product-state distribution of the NO fragment shows a similarity with the product-state distribution as predicted by the Franck-Condon overlap between a NO moiety of the dimer ion and a free NO. The dissociation dynamics seem to be independent of the NO internal energy. Finally, the dissociation dynamics reveal a correlation between the kinetic energy of the NO fragment and the degree of conservation of linear momentum between the O and N product atoms. The observations support a mechanism in which the recoil takes place along one of the NO bonds in the dimer.
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| 31. |
- Pettersson, Jan B. C., 1962, et al.
(författare)
-
Dissociative recombination and excitation of D-5(+) by collisions with low-energy electrons
- 2015
-
Ingår i: Molecular Physics. - : Informa UK Limited. - 0026-8976 .- 1362-3028. ; 113:15-16, s. 2099-2104
-
Tidskriftsartikel (refereegranskat)abstract
- We report results from high-resolution studies of D-5(+) cluster ion collisions with low-energy electrons performed in a heavy ion storage ring. Absolute dissociative recombination (DR) and dissociative excitation (DE) cross sections were determined for the energy range from 0.0005 to 20eV. The DR cross sections were exceedingly large at low energies, and DR resulted in efficient internal energy redistribution and pronounced fragmentation with two main product channels: D-2+3D (0.62 +/- 0.03) and 2D(2)+D (0.35 +/- 0.01). The DR and DE cross sections were comparable in the energy range from 0.2 to 20eV, which suggest that the two processes follow similar dynamics and are competing outcomes of the ion-electron interaction. A simple picture of the recombination process of D-5(+) which captures the essential physics is suggested. RAHAMSSON K, 1993, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM
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| 32. |
- Romero Lejonthun, Liza, 1973, et al.
(författare)
-
Chlorine interactions with water ice studied by molecular beam techniques.
- 2006
-
Ingår i: The journal of physical chemistry. B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:46, s. 23497-501
-
Tidskriftsartikel (refereegranskat)abstract
- The kinetics of chlorine interactions with ice at temperatures between 103 and 165 K have been studied using molecular beam techniques. The Cl(2) trapping probability is found to be unity at thermal incident energies, and trapping is followed by rapid desorption. The residence time on the surface is less than 25 microg at temperatures above 135 K and approaches 1 s around 100 K. Rate constants for desorption are determined for temperatures below 135 K. The desorption kinetics follow the Arrhenius equation, and activation energies of 0.24 +/- 0.03 and 0.31 +/- 0.01 eV, with corresponding preexponential factors of 10(12.08+/-1.19) and 10(16.52+/-0.38) s(-1), are determined. At least two different Cl(2) binding sites are concluded to exist on the ice surface. The observed activation energies are likely to be the Cl(2)-ice binding energies for these states, and the Cl(2)-surface interactions are concluded to be stronger than earlier theoretical estimates. The surface coverage of Cl(2) on ice under stratospheric conditions is estimated to be negligible, in agreement with earlier work.
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| 33. |
- Romero Lejonthun, Liza, 1973, et al.
(författare)
-
Formation of Adsorbed Layers by Deposition of Dinitrogen Pentoxide, Nitric Acid, and Water on Graphite
- 2009
-
Ingår i: J. Phys. Chem. C. - : American Chemical Society (ACS). ; 113, s. 7728-7734
-
Tidskriftsartikel (refereegranskat)abstract
- The formation of adsorbed layers of dinitrogen pentoxide, nitric acid, and water on graphite has been studied by molecular beam and light-scattering techniques. The desorption kinetics of N2O5 on graphite were described by the Arrhenius equation with an activation energy of 0.24 ± 0.03 eV and a pre-exponential factor of 2.3 × 10(10 ± 0.73) s−1, and N2O5 is concluded to bind more strongly than H2O to the graphite surface. Elastic helium scattering and light scattering were used to probe the formation of adlayers on the surface. Adsorption of pure N2O5 resulted in formation of thin adlayers at temperatures below 160 K. In coadsorption experiments N2O5 was concluded to facilitate the formation of thick N2O5−H2O ice layers at 155 K. In a similar way coadsorption of HNO3 and H2O resulted in the formation of thick adlayers at 170 K. N2O5 and HNO3 both bind more strongly than water to the graphite surface and are concluded to facilitate nucleation and growth of ice.
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| 34. |
- Romero Lejonthun, Liza, 1973, et al.
(författare)
-
Interactions of N2O5 and Related Nitrogen Oxides with Ice Surfaces: Desorption Kinetics and Collision Dynamics
- 2014
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:47, s. 13427-13434
-
Tidskriftsartikel (refereegranskat)abstract
- The detailed interactions of nitrogen oxides with ice are of fundamental interest and relevance for chemistry in cold regions of the atmosphere. Here, the interactions of NO, NO2, N2O4, and N2O5 with ice surfaces at temperatures between 93 and 180 K are investigated with molecular beam techniques. Surface collisions are observed to result in efficient transfer of kinetic energy and trapping of molecules on the ice surfaces. NO and NO2 rapidly desorb from pure ice with upper bounds for the surface binding energies of 0.16 +/- 0.02 and 0.26 +/- 0.03 eV, respectively. Above 150 K, N2O4 desorption follows first-order kinetics and is well described by the Arrhenius parameters E-a = 0.39 +/- 0.04 eV and A = 10((15.41.2)) s(1), while a stable N2O4 adlayer is formed at lower temperatures. A fraction of incoming N2O5 reacts to form HNO3 on the ice surface. The N2O5 desorption rates are substantially lower on pure water ice (Arrhenius parameters: Ea = 0.36 +/- 0.02 eV; A = 10(15.3 +/- 0.7) s(-1)) than on HNO3-covered ice (Ea = 0.24 +/- 0.02 eV; A = 10(11.5 +/- 0.7) s(-1)). The N2O5 desorption kinetics also sensitively depend on the sub-monolayer coverage of HNO3, with a minimum in N2O5 desorption rate at a low but finite coverage of HNO3. The studies show that none of the systems with resolvable desorption kinetics undergo ordinary desorption from ice, and instead desorption likely involves two or more surface states, with additional complexity added by coadsorbed molecules.
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| 35. |
- Ryding, Mauritz Johan, 1981, et al.
(författare)
-
Isotope exchange in reactions between D2O and size-selected ionic water clusters containing pyridine, H+(pyridine)m(H2O)n
- 2011
-
Ingår i: Physical Chemistry Chemical Physics. ; 13:4, s. 1356-1367
-
Tidskriftsartikel (refereegranskat)abstract
- Pyridine contg. water clusters, H+(pyridine)m(H2O)n, have been studied both exptl. by a quadrupole time-of-flight mass spectrometer and by quantum chem. calcns. In the expts., H+(pyridine)m(H2O)n with m = 1-4 and n = 0-80 are obsd. For the cluster distributions obsd., there are no magic nos., neither in the abundance spectra, nor in the evapn. spectra from size selected clusters. Expts. with size-selected clusters H+(pyridine)m(H2O)n, with m = 0-3, reacting with D2O at a center-of-mass energy of 0.1 eV were also performed. The cross-sections for H/D isotope exchange depend mainly on the no. of water mols. in the cluster and not on the no. of pyridine mols. Clusters having only one pyridine mol. undergo D2O/H2O ligand exchange, while H+(pyridine)m(H2O)n, with m = 2, 3, exhibit significant H/D scrambling. These results are rationalized by quantum chem. calcns. (B3LYP and MP2) for H+(pyridine)1(H2O)n and H+(pyridine)2(H2O)n, with n = 1-6. In clusters contg. one pyridine, the water mols. form an interconnected network of hydrogen bonds assocd. with the pyridinium ion via a single hydrogen bond. For clusters contg. two pyridines, the two pyridine mols. are completely sepd. by the water mols., with each pyridine being positioned diametrically opposite within the cluster. In agreement with exptl. observations, these calcns. suggest a "see-saw mechanism" for pendular proton transfer between the two pyridines in H+(pyridine)2(H2O)n clusters. [on SciFinder (R)]
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| 36. |
- Ryding, Mauritz Johan, 1981, et al.
(författare)
-
Proton mobility in water clusters
- 2012
-
Ingår i: European Journal of Mass Spectrometry. - : SAGE Publications. - 1469-0667 .- 1751-6838. ; 18:2, s. 215-222
-
Tidskriftsartikel (refereegranskat)abstract
- Proton mobility in water occurs quickly according to the so-called Grotthuss mechanism. This process and its elementary reaction steps can be studied in great detail by applying suitable mass spectrometric methods to ionic water clusters. Careful choice of suitable core ions in combination with analysis of cluster size trends in hydrogen/deuterium isotope exchange rates allows for detailed insights into fascinating dynamic systems. Analysis of the experiments has been promoted by extensive and systematic quantum chemical model calculations. Detailed low-energy mechanistic pathways for efficient water rearrangement and proton transfer steps, in particular cases along short preformed "wires" of hydrogen bonds, have been identified in consistency with experimental findings.
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| 37. |
- Ryding, Mauritz Johan, 1981, et al.
(författare)
-
Reactions of H+(pyridine)m(H2O)n and H+(NH3)1(pyridine)m(H2O)n with NH3: experiments and kinetic modelling
- 2012
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 12, s. 2809-2822
-
Tidskriftsartikel (refereegranskat)abstract
- Reactions between pyridine containing water cluster ions, H+(pyridine)1(H2O)n, H+(pyridine)2(H2O)n and H+(NH3)1(pyridine)1(H2O)n (n up to 15) with NH3 have been studied experimentally using a quadrupole time-of-flight mass spectrometer. The product ions in the reaction between H+(pyridine)m(H2O)n (m = 1 to 2) and NH3 have been determined for the first time. It is found that the reaction mainly leads to cluster ions of the form H+(NH3)1(pyridine)m(H2O)n-x, with x = 1 or 2 depending on the initial size of the reacting cluster ion. For a given number of water molecules (from 5 to 15) in the cluster ion, rate coefficients are found to be slightly lower than those for protonated pure water clusters reacting with ammonia. The rate coefficients obtained from this study are used in a kinetic cluster ion model under tropospheric conditions. The disagreement between ambient ground level measurements and previous models are discussed in relation to the results from our model and future experimental directions are suggested.
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| 38. |
- Salo, Kent, 1967, et al.
(författare)
-
Aerosol volatility and enthalpy of sublimation of carboxylic acids.
- 2010
-
Ingår i: The journal of physical chemistry. A. - : American Chemical Society (ACS). - 1520-5215 .- 1089-5639. ; 114:13, s. 4586-94
-
Tidskriftsartikel (refereegranskat)abstract
- The enthalpy of sublimation has been determined for nine carboxylic acids, two cyclic (pinonic and pinic acid) and seven straight-chain dicarboxylic acids (C(4) to C(10)). The enthalpy of sublimation was determined from volatility measurements of nano aerosol particles using a volatility tandem differential mobility analyzer (VTDMA) set-up. Compared to the previous use of a VTDMA, this novel method gives enthalpy of sublimation determined over an extended temperature range (DeltaT approximately 40 K). The determined enthalpy of sublimation for the straight-chain dicarboxylic acids ranged from 96 to 161 kJ mol(-1), and the calculated vapor pressures at 298 K are in the range of 10(-6)-10(-3) Pa. These values indicate that dicarboxylic acids can take part in gas-to-particle partitioning at ambient conditions and may contribute to atmospheric nucleation, even though homogeneous nucleation is unlikely. To obtain consistent results, some experimental complications in producing nanosized crystalline aerosol particles were addressed. It was demonstrated that pinonic acid "used as received" needed a further purification step before being suspended as a nanoparticle aerosol. Furthermore, it was noted from distinct differences in thermal properties that aerosols generated from pimelic acid solutions gave two types of particles. These two types were attributed to crystalline and amorphous configurations, and based on measured thermal properties, the enthalpy of vaporization was 127 kJ mol(-1) and that of sublimation was 161 kJ mol(-1). This paper describes a new method that is complementary to other similar methods and provides an extension of existing experimental data on physical properties of atmospherically relevant compounds.
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| 39. |
- Salo, Kent, 1967, et al.
(författare)
-
Thermal characterization of aminium nitrate nanoparticles.
- 2011
-
Ingår i: The journal of physical chemistry. A. - : American Chemical Society (ACS). - 1520-5215 .- 1089-5639. ; 115:42, s. 11671-7
-
Tidskriftsartikel (refereegranskat)abstract
- Amines are widely used and originate from both anthropogenic and natural sources. Recently, there is, in addition, a raised concern about emissions of small amines formed as degradation products of the more complex amines used in CO(2) capture and storage systems. Amines are bases and can readily contribute to aerosol mass and number concentration via acid-base reactions but are also subject to gas phase oxidation forming secondary organic aerosols. To provide more insight into the atmospheric fate of the amines, this paper addresses the volatility properties of aminium nitrates suggested to be produced in the atmosphere from acid-base reactions of amines with nitric acid. The enthalpy of vaporization has been determined for the aminium nitrates of mono-, di-, trimethylamine, ethylamine, and monoethanolamine. The enthalpy of vaporization was determined from volatility measurements of laboratory generated aerosol nanoparticles using a volatility tandem differential mobility analyzer set up. The determined enthalpy of vaporization for aminium nitrates range from 54 up to 74 kJ mol(-1), and the calculated vapor pressures at 298 K are around 10(-4) Pa. These values indicate that aminium nitrates can take part in gas-to-particle partitioning at ambient conditions and have the potential to nucleate under high NO(x) conditions, e.g., in combustion plumes.
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| 40. |
- Suter, Martina, 1966, et al.
(författare)
-
Argon collisions with amorphous water ice surfaces
- 2006
-
Ingår i: Chemical Physics. ; 326:2-3, s. 281-288
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics of argon atom collisions with amorphous ice surfaces are investigated using molecular beam techniques and molecular dynamics simulations. The formation of an amorphous ice layer on top of crystalline ice at 110 K is shown to have a strong influence on Ar scattering. Compared to crystalline ice, trapping followed by desorption is favoured over inelastic scattering, and a strongly enhanced emission of argon in the backward direction is observed. Molecular dynamics simulation with different types of amorphous and crystalline surfaces are consistent with the experimental data and show that large scale corrugation is required to reproduce the experimental findings. It is concluded that argon scattering can be used to probe changes in surface structure on the nanometer length-scale, while it is relatively insensitive to changes on the molecular level, and it thereby complements other techniques for studies of structural changes of ice surfaces. (c) 2006 Elsevier B.V. All rights reserved.
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| 41. |
- Suter, Martina, 1966, et al.
(författare)
-
Formation of water-ammonia ice on graphite studied by elastic helium scattering
- 2007
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 445, s. 208-212
-
Tidskriftsartikel (refereegranskat)abstract
- Helium and light scattering experiments have been performed to study the formation of water–ammonia ice layers on graphite at 110–160 K. Ice formation is mainly governed by the partial water pressure, but the presence of ammonia enhances the formation rate and influences the layer properties. Ice formed at temperatures <140 K wets the surface, while ice formed at higher temperatures does not. At temperatures around 140 K ammonia destabilizes the two-dimensional ice layers and a dewetting transition is observed at a surface coverage of 90–95%.
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| 42. |
- Suter, Martina, 1966, et al.
(författare)
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Molecular Beam studies of Carbon Monoxide Interactions with Water Ice.
- 2004
-
Ingår i: Physica Scripta. ; T110:doi:10.1238/Physica.Topical.110a00350, s. 350-354
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics of CO interactions with water ice surfaces are studied using molecular beam techniques. The experimental method allows for detailed investigations of interaction between molecules and ice surfaces under single collision conditions, and collision dynamics and energy transfer are characterized. An ice surface is prepared by deposition of water vapor on a cold substrate and the surface is maintained in a vacuum chamber with a partial water vapor pressure up to 10-4 mbar, which allows for experiments with ice surfaces in the temperature range 100–190 K. A molecular beam is directed towards the ice surface, and the molecular flux from the surface is detected by mass spectrometry. Angular-resolved intensity and time-of-flight distributions are measured, and the effects of surface temperature, incident translational energy and incident angle are investigated. The surface collisions are highly inelastic with large energy loss observed for the directly scattered flux, similar to the results for the previously studied Ar-ice and HCl-ice systems. The data for the energy loss as a function of scattering angle show that energy transfer is substantial both parallel and perpendicular to the surface plane. The trapping of CO on the surface is found to be very effective under typical thermal conditions. The molecules accommodate to the temperature of the ice, but rapidly leave the surface by desorption because of the low binding energy to the surface.
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| 43. |
- Suter, Martina, 1966, et al.
(författare)
-
Surface properties of water ice at 150-191 K studied by elastic helium scattering.
- 2006
-
Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:17
-
Tidskriftsartikel (refereegranskat)abstract
- A highly surface sensitive technique based on elastic scattering of low-energy helium atoms has been used to probe the conditions in the topmost molecular layer on ice in the temperature range of 150-191 K. The elastically scattered intensity decreased slowly as the temperature was increased to about 180 K, followed by a rapid decrease at higher temperatures. An effective surface Debye temperature of 185+/-10 K was calculated from the data below 180 K. The changes in the ice surface above 180 K are interpreted as the onset of an anomalous enhancement of the mean square vibrational amplitude for the surface molecules and/or the onset of a limited amount of disorder in the ice surface. The interpretation is consistent with earlier experimental studies and molecular dynamics simulations. The observed changes above 180 K can be considered as the first sign of increased mobility of water molecules in the ice surface, which ultimately leads to the formation of a quasiliquid layer at higher temperatures. A small shift and broadening of the specular peak was also observed in the range of 150-180 K and the effect is explained by the inherent corrugation of the crystalline ice surface. The peak shift became more pronounced with increasing temperature, which indicates that surface corrugation increases as the temperature approaches 180 K. The results have implications for the properties and surface chemistry of atmospheric ice particles, and may contribute to the understanding of solvent effects on the internal molecular motion of hydrated proteins and other organic structures such as DNA.
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| 44. |
- Svane, Maria, 1957, et al.
(författare)
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On-Line Chemical Analysis of Individual Alkali-Containing Aerosol Particles by Surface Ionization Combined with Time-of-Flight Mass Spectrometry
- 2009
-
Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 43:7, s. 653-661
-
Tidskriftsartikel (refereegranskat)abstract
- An aerosol mass spectrometer for measurements of the alkali metal content in individual submicron aerosol particles is presented. The instrument combines surface ionization of individual particles on a hot platinum surface with orthogonal acceleration time-of-flight mass spectrometry. The instrument simultaneously provides the content of different alkali metal elements in single particles with high sensitivity. The instrument is characterized in laboratory experiments, and determination of the alkali metal content is demonstrated for particle diameters of 50-500 nm. The technique is demonstrated in ambient air measurements at an urban background site, and sea spray particles and particles originating from biomass burning are identified based on their content of sodium and potassium. Possible further improvements and applications of the technique are discussed.
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| 45. |
- Thomson, Erik S, et al.
(författare)
-
Collision Dynamics and Solvation of Water Molecules in a Liquid Methanol Film
- 2011
-
Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 2:17, s. 2174-2178
-
Tidskriftsartikel (refereegranskat)abstract
- Environmental molecular beam experiments are used to examine water interactions with liquid methanol films at temperatures from 170 to 190 K. We find that water molecules with 0.32 eV incident kinetic energy are efficiently trapped by the liquid methanol. The scattering process is characterized by an efficient loss of energy to surface modes with a minor component of the incident beam that is inelastically scattered. Thermal desorption of water molecules has a well characterized Arrhenius form with an activation energy of 0.47 ± 0.11 eV and pre-exponential factor of 4.6 × 10^(15±3) s^(–1). We also observe a temperature-dependent incorporation of incident water into the methanol layer. The implication for fundamental studies and environmental applications is that even an alcohol as simple as methanol can exhibit complex and temperature-dependent surfactant behavior.
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| 46. |
- Vigren, Erik, et al.
(författare)
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Dissociative recombination of fully deuterated protonated acetonitrile, CD3CND+ : Product branching fractions, absolute cross section and thermal rate coefficient
- 2008
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 10, s. 4014-4019
-
Tidskriftsartikel (refereegranskat)abstract
- The dissociative recombination of fully deuterated protonated acetonitrile, CD3CND+, has been investigated at the CRYRING heavy ion storage ring, located at the Manne Siegbahn Laboratory, Stockholm, Sweden. Branching fractions were measured at similar to 0 eV relative collision energy between the ions and the electrons and in 65% of the DR events there was no rupture of bonds between heavy atoms. In the remaining 35%, one of the bonds between the heavy atoms was broken. The DR cross-section was measured between similar to 0 eV and 1 eV relative collision energy. In the energy region between 1 meV and 0.1 eV the cross section data were best fitted by the expression sigma = 7.37 x 10(-16) (E/eV)(-1.23) cm(2), whereas sigma = 4.12 x 10(-16) (E/eV)(-1.46) cm(2) was the best fit for the energy region between 0.1 and 1.0 eV. From the cross section a thermal rate coefficient of alpha(T) = 8.13 x 10(-7) (T/300)(-0.69) cm(3) s(-1) was deduced.
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| 47. |
- Zatula, Alexey, et al.
(författare)
-
Proton mobility and stability of water clusters containing the bisulfate anion, HSO4-(H2O)n
- 2011
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 13:29, s. 13287-13294
-
Tidskriftsartikel (refereegranskat)abstract
- Bisulfate water clusters, HSO(4)-(H(2)O)(n), have been studied both experimentally by a quadrupole time-of-flight mass spectrometer and by quantum chemical calculations. For the cluster distributions studied, there are some possible "magic number" peaks, although the increase in abundance compared to their neighbours is small. Experiments with size-selected clusters with n = 0-25, reacting with D(2)O at a center-of-mass energy of 0.1 eV, were performed, and it was observed that the rate of hydrogen/deuterium exchange is lower for the smallest clusters (n < 8) than for the larger (n > 11), with a transition taking place in the range n = 8-11. We propose that the protonic defect of the bisulfate ion remains rather stationary unless the degree of hydration reaches a given level. In addition, it was observed that H/D scrambling becomes close to statistically randomized for the larger clusters. Insight into this size dependency was obtained by B3LYP/6-311++G(2d, 2p) calculations for HSO(4)(-)(H(2)O)(n) with n = 0-10. In agreement with experimental observations, these calculations suggest pronounced effectiveness of a "see-saw mechanism" for pendular proton transfer with increasing HSO(4)(-)(H(2)O)(n) cluster size.
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| 48. |
- Öjekull, Jenny, 1973, et al.
(författare)
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Dissociative recombination of ammonia clusters studied by storage ring experiments
- 2006
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:19, s. 194306-
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Tidskriftsartikel (refereegranskat)abstract
- Dissociative recombination of ammonia cluster ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for dissociative recombination of H+(NH3)(2), H+(NH3)(3), D+(ND3)(2), and D+(ND3)(3) in the collision energy range of 0.001-27 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 1000 K are calculated from the experimental data and compared with earlier results. The fragmentation patterns for the two ions H+(NH3)(2) and D+(ND3)(2) show no clear isotope effect. Dissociative recombination of X+(NX3)(2) (X=H or D) is dominated by the product channels 2NX(3)+X [0.95 +/- 0.02 for H+(NH3)(2) and 1.00 +/- 0.02 for D+(ND3)(2)]. Dissociative recombination of D+(ND3)(3) is dominated by the channels yielding three N-containing fragments (0.95 +/- 0.05).
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| 49. |
- Öjekull, Jenny, 1973, et al.
(författare)
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Dissociative recombination of H+(H2O)3 and D+(D2O)3 water cluster ions with electrons: Cross sections and branching ratios
- 2007
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Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127, s. 194301-194309
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Tidskriftsartikel (refereegranskat)abstract
- Dissociative recombination (DR) of the water cluster ions H+(H2O)3 and D+(D2O)3 with electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). For the first time, absolute DR cross sections have been measured for H+(H2O)3 in the energy range of 0.001–0.8 eV, and relative cross sections have been measured for D+(D2O)3 in the energy range of 0.001–1.0 eV. The DR cross sections for H+(H2O)3 are larger than previously observed for H+(H2O)n (n=1,2), which is in agreement with the previously observed trend indicating that the DR rate coefficient increases with size of the water cluster ion. Branching ratios have been determined for the dominating product channels. Dissociative recombination of H+(H2O)3 mainly results in the formation of 3H2O+H (probability of 0.95±0.05) and with a possible minor channel resulting in 2H2O+OH+H2 (0.05±0.05). The dominating channels for DR of D+(D2O)3 are 3D2O+D (0.88±0.03) and 2D2O+OD+D2 (0.09±0.02). The branching ratios are comparable to earlier DR results for H+(H2O)2 and D+(D2O)2, which gave 2X2O+X (X=H,D) with a probability of over 0.9.
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| 50. |
- Öjekull, Jenny, 1973, et al.
(författare)
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Dissociative recombination of NH4+ and ND4+ ions : Storage ring experiments and ab initio molecular dynamics
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:16, s. 7391-7399
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Tidskriftsartikel (refereegranskat)abstract
- The dissociative recombination (DR) process of NH4+ and ND4+ molecular ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for DR of NH4+ and ND4+ in the collision energy range 0.001-1 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 2000 K are calculated from the experimental data. The absolute cross section for NH4+ agrees well with earlier work and is about a factor of 2 larger than the cross section for ND4+. The dissociative recombination of NH4+ is dominated by the product channels NH3+H (0.85+/-0.04) and NH2+2H (0.13+/-0.01), while the DR of ND4+ mainly results in ND3+D (0.94+/-0.03). Ab initio direct dynamics simulations, based on the assumption that the dissociation dynamics is governed by the neutral ground-state potential energy surface, suggest that the primary product formed in the DR process is NH3+H. The ejection of the H atom is direct and leaves the NH3 molecule highly vibrationally excited. A fraction of the excited ammonia molecules may subsequently undergo secondary fragmentation forming NH2+H. It is concluded that the model results are consistent with gross features of the experimental results, including the sensitivity of the branching ratio for the three-body channel NH2+2H to isotopic exchange.
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