| 1. |
- Steinbach, C, et al.
(författare)
-
Detection of the Book Isomer from the OH-stretch Spectroscopy of Size Selected Water Hexamers.
- 2004
-
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.
|
|
| 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.
|
|
| 3. |
- Al-Khalili, A, et al.
(författare)
-
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
-
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.
|
|
| 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.
|
|
| 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).
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
