SwePub - sökning: WFRF:(Hansen Klavs)

Numrering	Referens	Omslagsbild	Hitta
51.	Hansen, Klavs, 1958, et al. (författare) Non-scrambling of hydrogen in NH4+(H2O)3 clusters 2019 Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 9, s. 6620-6626 Tidskriftsartikel (refereegranskat)abstract We have measured the metastable decay of protonated, ammonia-doped, deuterated water clusters produced in an electrospray source, dn-NH4 +(H2O)3, n ¼ 0–6. The mass spectra show a very strong odd–even effect, consistent with a low degree of scrambling of the hydrogen bound to water and to the ammonia. The relative evaporation rate constant for light water was almost twice the one for heavy water, with the rate for mixed protium–deuterium water molecule intermediate between these two values.
52.	Hansen, Klavs, 1958, et al. (författare) Obtaining colder ensembles of free clusters by using evaporation and recoil 2005 Ingår i: Eur. Phys. J. D. - : Springer Science and Business Media LLC. - 1434-6060. ; 32, s. 339-345 Tidskriftsartikel (refereegranskat)abstract We describe a theoretical model which treats the effects of evaporation-induced recoil on the mass and temperature distributions of a collimated beam of small neutral clusters emitted by a hot-nozzle source. The model incorporates two important consequences of in-flight cluster fragmentation processes. One is the well-known statistical evaporation of atoms and dimers accompanied by cluster size redistribution and cooling, and the other is the accompanying mechanical recoil of the fragments. We predict that the filtering effect introduced by cluster recoil can be used to an advantage by separating out the off-axis cluster population. This fraction will have a significantly narrower and colder distribution of internal temperatures than the on-axis ensemble.
53.	Hansen, Klavs, 1958, et al. (författare) Single Photon Thermal Ionization of C60 2017 Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 118 Tidskriftsartikel (refereegranskat)abstract We report on experiments which show that C60 can ionize in an indirect, quasithermal boiloff process after absorption of a single photon. The process involves a large number of incoherently excited valence electrons and yields electron spectra with a Boltzmann distribution with temperatures exceeding 104 K. It is expected to be present for other molecules and clusters with a comparatively large number of valence electrons. The astrophysical consequences are briefly discussed.
54.	Hansen, Klavs, 1958, et al. (författare) Single photon thermal ionization of large molecules 2017 Ingår i: Elettra Highlights. Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract We have demonstrated that gas phase C60 can ionize in a quasi-thermal process where the absorption of a single photon at energies of several tens of eVs leads to the formation of a transient hot electron gas, while the vibrational degrees of freedom remain cold. The existence of the hot electron gas is signalled by the emission of thermal electrons with Boltzmann-like kinetic energy distributions with temperatures of 10000−20000 K. The ionization mechanism is expected to be general for large molecules and will have, e.g., astrophysical consequences.
55.	Hansen, Klavs, 1958 (författare) Single photon transient hot electron ionization of C60 2017 Ingår i: Physical Chemistry Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:30, s. 19699-19706 Tidskriftsartikel (refereegranskat)abstract Recent experiments have demonstrated that C60 can ionize in a thermal process after absorption of a photon with energy far above the ionization energy. This indirect ionization mechanism is investigated here by calculating the total and singly charged ion yields, electron energy distributions, and effective electronic temperatures as a function of photon energy.
56.	Hansen, Klavs, 1958, et al. (författare) Spontaneous decay of small copper-cluster anions Cun− (n=3–6), on long time scales 2017 Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 95:2 Tidskriftsartikel (refereegranskat)abstract We have measured the spontaneous neutral particle emission from copper-cluster anions (Cun −, n = 3–6) stored at cryogenic temperatures in one of the electrostatic ion storage rings of the Double ElectroStatic Ion Ring ExpEriment facility at Stockholm University. The measured rate of emission from the stored Cu3 − ions follows a single power-law decay for about 1 ms but then decreases much more rapidly with time. The latter behavior may be due to a decrease in the density of available final states in Cu3 as the excitation energies of the decaying ions approach the electron detachment threshold. The emissions from Cu4 −, Cu5−, and Cu6− are well described by sums of two power laws that are quenched by radiative cooling of the stored ions with characteristic times between a few and hundreds of milliseconds. We relate these two-component behaviors to populations of stored ions with higher and lower angular momenta. In a separate experiment, we studied the laser-induced decay of Cu6− ions that were excited by 1.13- or 1.45-eV photons after 46 ms of storage.
57.	Hansen, Klavs, 1958, et al. (författare) Stability and dissociation pathways of doped AunX+ clusters (X=Y,Er,Nb) 2008 Ingår i: Faraday Discussion. ; 138 Tidskriftsartikel (refereegranskat)abstract Size dependent stabilities, fragmentation pathways and dissociation energies of a series of gas phase cationic doped gold clusters, AunX+ (5 < n < 20; X = Y, Er and Nb), and pure Aun+ clusters were investigated in photofragmentation experiments. Size dependent stability patterns were obtained and the branching between monomer and dimer evaporation was studied. For bare gold, the competing neutral monomer and dimer evaporation channels were found in agreement with earlier studies. For doped clusters, monomer evaporation is the most likely fragmentation channel with the exception of Au18Y+ and Au20Y+ for which gold dimer evaporation is also observed. Relations between the evaporative activation energies and both the experimental abundances and the fragment yield were derived based on unimolecular rate constants. The dissociation energies from this analysis show an odd-even staggering and enhanced stabilities for certain cluster sizes, in agreement with simple electronic shell model predictions.
58.	Hansen, Klavs, 1958 (författare) Statistical physics of nanoparticles in the gas phase 2013 Bok (övrigt vetenskapligt/konstnärligt)abstract Thermal processes are ubiquitous and an understanding of thermal phenomena is essential for a complete description of the physics of nanoparticles, both for the purpose of modeling the dynamics of the particles and for the correct interpretation of experimental data. This book has the twofold aim to present coherently the relevant results coming from the recent scientific literature and to guide the readers through the process of deriving results, enabling them to explore the limits of the mathematical approximations and test the power of the method. The book is focused on the fundamental properties of nanosystems in the gas phase. For this reason there is a strong emphasis on microcanonical physics. Each chapter is enriched with exercises and 3 Appendices provide additional useful materials.
59.	Hansen, Klavs, 1958 (författare) Statistical physics of nanoparticles in the gas phase 2018 Bok (övrigt vetenskapligt/konstnärligt)abstract Several changes have been made to the text in this second edition relative to the first, and no chapter has been left untouched in the process. The changes are of two types. One is an expansion of the scope of the material covered. The other is the introduction of new developments of the field. The revisions have resulted in two new chapters and several new sections. In addition to these changes, uncountably many minor changes have been made in figures and in the text to improve readability. A part of the preparation of this edition was the correction of the errors and (mostly) misprints spotted in the first edition. During this process, it became clear to me that while two errors may cancel each other, mistakes never do. Happily, most mistakes were of minor importance. The idea behind the book remains unchanged: To provide a guided tour of a number of interesting phenomena in the field. A reader who compares this edition with the first will realize that occasionally the presentation has changed radically. But although the flavor may have changed here and there, hopefully the nutritional value still makes it worth for the reader to consume the dish. I want to thank Takeshi Furukawa, Bernd von Issendorff, Vitali Zhaunerchyk, and Mathias Weber for providing illustrative experimental data; Petr Slavícĕk for an educational conversation on holy water at an Erice Workshop; and Hanna Vehkamäki for enlightening me on the first nucleation theorem. Corrections, suggestions, and error reports are welcome and can be mailed to me at klavshansen@tju.edu.cn.
60.	Hansen, Klavs, 1958 (författare) The classical capture cross section of an electron and neutral and anionic polarizable molecules with permanent dipole moments 2019 Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806. ; 438, s. 142-147 Tidskriftsartikel (refereegranskat)abstract tThe energy dependent capture cross sections of electrons and polarizable neutral molecules with perma-nent dipole moments and with and without an additional negative charge are calculated classically. Theresults can be expressed in lengths and energies scaled with parameters that derive from the polarizabil-ity, dipole moment and charge. Cross sections integrated over impact angles are given. The results are ofinterest for both electron attachment and for thermal electron emission. The consequences for thermalelectron emission spectra are discussed quantitatively.
61.	Hansen, Klavs, 1958, et al. (författare) The dissociation energy of V13+ and the consequences for radiative cooling 2005 Ingår i: Eur. Phys. J. D. - : Springer Science and Business Media LLC. - 1434-6060. ; 34, s. 67-71 Tidskriftsartikel (refereegranskat)abstract The dissociation energy of V13+ has been determined by comparison of the rates of sequential fragmentation, V13+→V 12+→V 11+, and single-step fragmentation of the first fragment, V12+→V 11+. The dissociation-energy value obtained as D=4.35(13) eV has implications for the amount of radiative cooling of the cluster derived form the data presented earlier [C. Walther et al., Phys. Rev. Lett. 83, 3816 (1999)] and is used to analyze additional results.
62.	Hansen, Klavs, 1958 (författare) The effective temperature in microcanonical rate constants 2015 Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 620, s. 43-45 Tidskriftsartikel (refereegranskat)abstract Microcanonical rate constants can be parameterized in terms of an effective temperature. We show here that for fairly general level densities of the involved species it is possible to make this parametrization with a temperature independent heat capacity and a rate constant of the Arrhenius form. This is a major simplification in the interpretation of many experiments on unimolecular decay in vacuum. The results show that activation energies and heat capacities measured in microcanonical experiment differ from their canonical analogues.
63.	Hansen, Klavs, 1958, et al. (författare) The frequency factor in statistical fullerene decay 2006 Ingår i: Int. J. Mass Spec.. - : Elsevier BV. - 1387-3806. ; 252, s. 79-95 Tidskriftsartikel (refereegranskat)abstract Experiments on fullerene decay are reviewed and the frequency factor for C2 emission is extracted. The value is also calculated theoretically. Inclusion of a number of previously disregarded degrees of freedom for the products increase the theoretical estimate for C60 to above 1020 s−1, in good agreement with experimental results.
64.	Hansen, Klavs, 1958 (författare) Thermal damping of odd-even effects in gold clusters 2020 Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 530 Tidskriftsartikel (refereegranskat)abstract The amplitude of the odd-even variation in binding energy is calculated for cationic gold clusters, Au+n , n = 8 26, extracted from experimental literature data. The data are found to agree fairly well with a simple Fermi gas estimate. Motivated by this, the canonical ensemble free energies are calculated for a ladder spectrum. Experimentally observed differences in ground state dissociation free energies between species with odd and even numbers of valence electrons reach the high temperature limit at temperatures significantly below values corresponding to the HOMO-LUMO gap. Remarkably, the asymptotic high temperature limit does not correspond to the complete disappearance of the zero temperature free energy difference. Likewise, the amount of electronically excited states are significantly higher than a simple estimate based on the Boltzmann factor of the gap energy, having implications for threshold ionization yields.
65.	Hansen, Klavs, 1958, et al. (författare) Thermal radiation of gold clusters on microsecond time scales 2017 Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 96 Tidskriftsartikel (refereegranskat)abstract Small positively charged gold clusters have been found to emit thermal radiation at a very high rate, with time constants ranging from one to 35μs for Aun + (n = 6–13,15). For sizes n = 14,16–20 the radiation occurs on much longer time scales. Strong thermal suppression of the population of higher-lying states puts constraints on the possible energies of excited states that can contribute to the radiation. Taking that into account, an evaluation of the experimentally determined rate constants shows that the strong radiation originates from thermally excited low-lying electronic states hitherto not observed. The origin of these states is discussed and two possibilities are suggested: one is related to electron correlation and electron pairing, and the other results from thermal shape fluctuations.
66.	Hansen, Klavs, 1958, et al. (författare) Thermal radiation of laser heated niobium clusters Nb_N+, 8 ≤ N ≤ 22 2014 Ingår i: Journal of Chemical Physics. - 0021-9606 .- 1089-7690. ; 141 Tidskriftsartikel (refereegranskat)abstract The thermal radiation from small, laser heated, positively charged niobium clusters has been measured. The emitted power was determined by the quenching effect on the metastable decay, employing two different experimental protocols. The radiative power decreases slightly with cluster size and shows no strong size-to-size variations. The magnitude is 40–50 keV/s at the timescale of several microseconds, which is the measured crossover time from evaporative to radiative cooling.
67.	Hansen, Klavs, 1958 (författare) Tunneling and reflection in unimolecular reaction kinetic energy release distributions 2018 Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 693, s. 66-71 Tidskriftsartikel (refereegranskat)abstract The kinetic energy release distributions in unimolecular reactions is calculated with detailed balance theory, taking into account the tunneling and the reflection coefficient in three different types of transition states; (i) a saddle point corresponding to a standard RRKM-type theory, (ii) an attachment Langevin cross section, and (iii) an absorbing sphere potential at short range, without long range interactions. Corrections are significant in the one dimensional saddle point states. Very light and lightly bound absorbing systems will show measurable effects in decays from the absorbing sphere, whereas the Langevin cross section is essentially unchanged.
68.	Hansen, Mette, et al. (författare) Effect of Whey Protein Hydrolysate on Performance and Recovery of Top-Class Orienteering Runners. 2015 Ingår i: International Journal of Sport Nutrition & Exercise Metabolism. - : Human Kinetics. - 1526-484X .- 1543-2742. ; 25:2 Tidskriftsartikel (refereegranskat)abstract This trial aimed to examine the effect of whey protein hydrolysate intake before and after exercise sessions on endurance performance and recovery in elite orienteers during a training camp. Eighteen elite orienteers participated in a randomized controlled intervention trial during a 1-week training camp (13 exercise sessions). Half of the runners (PRO-CHO) ingested a protein drink before (0.3 g kg−1) and a protein-carbohydrate drink after (0.3 g protein kg−1 and 1 g carbohydrate kg−1) each exercise session. The others ingested energy and timematched carbohydrate drinks (CHO). A 4-km run-test with 20 control points was performed before and on the last day of the intervention. Blood and saliva were obtained in the mornings, before and after run-tests, and after the last training session. During the intervention, questionnaires were fulfilled regarding psychological sense of performance capacity and motivation. PRO-CHO and not CHO improved performance in the 4-km run-test (interaction p < .05). An increase in serum creatine kinase was observed during the week, which was greater in CHO than PRO-CHO (interactionp < .01). Lactate dehydrogenase (p < .001) and cortisol (p = .057) increased during the week, but the change did not differ between groups. Reduction in sense of performance capacity during the intervention was greater in CHO (p < .05) than PRO-CHO. In conclusion, ingestion of whey protein hydrolysate before and after each exercise session improves performance and reduces markers of muscle damage during a strenuous 1-week training camp. The results indicate that protein supplementation in conjunction with each exercise session facilitates the recovery from strenuous training in elite orienteers.
69.	Hansen, M., et al. (författare) Protein intake during training sessions has no effect on performance and recovery during a strenuous training camp for elite cyclists 2016 Ingår i: Journal of the International Society of Sports Nutrition. - : Informa UK Limited. - 1550-2783. ; 13:9 Tidskriftsartikel (refereegranskat)abstract Background: Training camps for top-class endurance athletes place high physiological demands on the body. Focus on optimizing recovery between training sessions is necessary to minimize the risk of injuries and improve adaptations to the training stimuli. Carbohydrate supplementation during sessions is generally accepted as being beneficial to aid performance and recovery, whereas the effect of protein supplementation and timing is less well understood. We studied the effects of protein ingestion during training sessions on performance and recovery of elite cyclists during a strenuous training camp. Methods: In a randomized, double-blinded study, 18 elite cyclists consumed either a whey protein hydrolysate-carbohydrate beverage (PRO-CHO, 14 g protein/h and 69 g CHO/h) or an isocaloric carbohydrate beverage (CHO, 84 g/h) during each training session for six days (25-29 h cycling in total). Diet and training were standardized and supervised. The diet was energy balanced and contained 1.7 g protein/kg/day. A 10-s peak power test and a 5-min all-out performance test were conducted before and after the first training session and repeated at day 6 of the camp. Blood and saliva samples were collected in the morning after overnight fasting during the week and analyzed for biochemical markers of muscle damage, stress, and immune function. Results: In both groups, 5-min all-out performance was reduced after the first training session and at day 6 compared to before the first training session, with no difference between groups. Peak power in the sprint test did not change significantly between tests or between groups. In addition, changes in markers for muscle damage, stress, and immune function were not significantly influenced by treatment. Conclusions: Intake of protein combined with carbohydrate during cycling at a training camp for top cyclists did not result in marked performance benefits compared to intake of carbohydrates when a recovery drink containing adequate protein and carbohydrate was ingested immediately after each training session in both groups. These findings suggest that the addition of protein to a carbohydrate supplement consumed during exercise does not improve recovery or performance in elite cyclists despite high demands of daily exhaustive sessions during a one-week training camp.
70.	Hartman, Henrik, et al. (författare) First storage of ion beams in the Double Electrostatic Ion-Ring Experiment : DESIREE 2013 Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 84:5 Tidskriftsartikel (refereegranskat)abstract We report on the first storage of ion beams in the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. We have produced beams of atomic carbon anions and small carbon anion molecules (Cn-, n = 1, 2, 3, 4) in a sputter ion source. The ion beams were accelerated to 10 keV kinetic energy and stored in an electrostatic ion storage ring enclosed in a vacuum chamber at 13 K. For 10 keV C2- molecular anions we measure the residual-gas limited beam storage lifetime to be 448 s +/- 18 s with two independent detector systems. Using the measured storage lifetimes we estimate that the residual gas pressure is in the 10-14 mbar range. When high current ion beams are injected, the number of stored particles does not follow a single exponential decay law as would be expected for stored particles lost solely due to electron detachment in collision with the residual-gas. Instead, we observe a faster initial decay rate, which we ascribe to the effect of the space charge of the ion beam on the storage capacity.
71.	Hartman, Henrik, et al. (författare) Negative ion relaxation and reactions in a cryogenic storage ring 2020 Ingår i: Journal of Physics: Conference Series Vol 1412. - : IOP Publishing. - 1742-6588 .- 1742-6596. Konferensbidrag (refereegranskat)abstract An overview of recent experimental results of studies of negative atomic and molecular ions in the Double ElectroStatic Ion-Ring ExpEriment, DESIREE is given. Metastable level lifetimes in atomic negative ions have been measured by time-dependent laser photodetachment. Rotational relaxation of diatomic anions is studied by near-threshold photodetachment. Spontaneous decays of small metal cluster anions by electron emission and fragmentation is studied with decay-channel specificity. Finally, mutual neutralisation of pairs of negative and positive ions has been investigated with initial and final state selectivity.
72.	Hedén, Martin, 1976, et al. (författare) Molecular Fusion of (C60)N Clusters in the Gas Phase after Femtosecond Laser Irradiation 2005 Ingår i: Phys. Rev. A. - 1050-2947. ; 71 Tidskriftsartikel (refereegranskat)abstract We report observation of molecular fusion of (C60)N+ clusters to form large fullerene molecules after excitation by 800-nm femtosecond laser pulses. The fused species decay by undergoing C2 fragmentation. Such fragmentation behavior for excited clusters of fullerene molecules can be understood in terms of the energetics of molecular fusion as determined previously from fullerene-fullerene collision experiments. Within a certain excitation energy window, there is sufficient time for a substantial atomic rearrangement to take place within the clusters before they dissociate. Below this energy window there is not sufficient internal energy for molecular fusion to occur while above the energy window multiple ionization followed by breakup of the clusters dominates.
73.	Hedén, Martin, 1976, et al. (författare) Molecular fusion within fullerene clusters induced by femtosecond laser excitation 2007 Ingår i: Eur.Phys.J. D. - 1434-6060. ; 43 Tidskriftsartikel (refereegranskat)
74.	Hedén, Martin, 1976, et al. (författare) Thermal radiation from CN+ and La@CN 2005 Ingår i: J. Chem. Phys.. - : AIP Publishing. - 0021-9606. ; 123 Tidskriftsartikel (refereegranskat)abstract The radiative cooling of positively charged fullerene and endohedral fullerene fragments of C60, C70, C84, and La@C82 has been measured in a time-of-flight mass spectrometer. The radiative cooling is measured via its influence on the metastable decay. The emissivity extracted from the data is between 4×10–4 and 13×10–4. These values agree fairly well with the emissivity calculated from considering the low-energy tail of the surface plasmon. No major difference is found in the emission behavior of empty and endohedral fullerenes.
75.	Ito, G., et al. (författare) Cooling Dynamics of Photoexcited C6 − and C6H− 2014 Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 112 Tidskriftsartikel (refereegranskat)abstract We report conclusive evidence of an efficient cooling mechanism via the electronic radiative transitions of hot small molecular anions isolated in vacuum. We stored C6− and C6H− in an ion storage ring and observed laser-induced electron detachment with delays up to several milliseconds. The terminal hydrogen atom caused a drastic change in the decay profiles. The decay of hotoexcited C6H− is slow and nonexponential, which can be explained by depletion cooling, whereas that for C6− occurs extremely fast, on a time scale below 0.1 ms and can only be explained by electronic radiative cooling via low-lying electronic excited states.
76.	Ito, Gen, et al. (författare) Difference in cooling dynamics between photo-excited C6- and C6H- 2014 Ingår i: Journal of Physics, Conference Series. - 1742-6588 .- 1742-6596. ; 488 Tidskriftsartikel (refereegranskat)abstract Laser-induced electron detachment of C6- and C6H- stored in an ion storage ring was observed respectively, focusing attention onto the delayed processes with the time constants up to several milliseconds. We found the drastic difference in the decay profiles of photo-excited C6- and C6H- that is, C6- decayed much faster than C6H-. The unexpected fast decay of C6- indicates that it is governed by the radiative cooling with electronic transitions rather than vibrational nor depletion cooling.
77.	Johansson, J. O., et al. (författare) Anisotropic hot electron emission from fullerenes 2012 Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 136:16 Tidskriftsartikel (refereegranskat)abstract Photoelectron spectra for fullerenes C-60 and C-70 ionized using 800 nm laser pulses with pulse durations from 120 to 1000 fs show thermal electron kinetic energy distributions but they also exhibit angular anisotropy with respect to the laser light polarization. The effective temperature of electrons, measured along the laser polarization direction, is significantly higher than in the perpendicular direction. We explain this observation by considering that the emission of the thermal electrons is uncorrelated with the phase of the laser pulse, unlike directly ionized electrons, and, depending on the time of emission, they may experience an additional "kick" from the vector potential of the laser field when they are emitted from the molecule. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704828]
78.	Kadhane, U., et al. (författare) Near-infrared photoabsorption by C-60 dianions in a storage ring 2009 Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131:1 Tidskriftsartikel (refereegranskat)abstract We present a detailed study of the electronic structure and the stability of C-60 dianions in the gas phase. Monoanions were extracted from a plasma source and converted to dianions by electron transfer in a Na vapor cell. The dianions were then stored in an electrostatic ring, and their near-infrared absorption spectrum was measured by observation of laser induced electron detachment. From the time dependence of the detachment after photon absorption, we conclude that the reaction has contributions from both direct electron tunneling to the continuum and vibrationally assisted tunneling after internal conversion. This implies that the height of the Coulomb barrier confining the attached electrons is at least similar to 1.5 eV. For C-60(2-) ions in solution electron spin resonance measurements have indicated a singlet ground state, and from the similarity of the absorption spectra we conclude that also the ground state of isolated C-60(2-) ions is singlet. The observed spectrum corresponds to an electronic transition from a t(1u) lowest unoccupied molecular orbital (LUMO) of C-60 to the t(1g) LUMO+1 level. The electronic levels of the dianion are split due to Jahn-Teller coupling to quadrupole deformations of the molecule, and a main absorption band at 10723 cm(-1) corresponds to a transition between the Jahn-Teller ground states. Also transitions from pseudorotational states with 200 cm(-1) and (probably) 420 cm(-1) excitation are observed. We argue that a very broad absorption band from about 11 500 cm(-1) to 13 500 cm(-1) consists of transitions to so-called cone states, which are Jahn-Teller states on a higher potential-energy surface, stabilized by a pseudorotational angular momentum barrier. A previously observed, high-lying absorption band for C-60(-) may also be a transition to a cone state.
79.	Kaminska, M., et al. (författare) Radiative cooling of hot C_n and C_nH^- molecules 2015 Ingår i: Journal of Physics, Conference Series. - 1742-6588 .- 1742-6596. ; 635 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract We have measured the rates of neutrals produced from 10 keV C_n or C_nH (n=2, 4, 6, 8, and 10) ion beams stored in one of DESIREE's 14 K storage rings. For n=4, 6, and 8 we observe marked differences between C_n and CnH cooling rates as inverse internal conversion [cf. S. Martin et al (2013) Phys. Rev. Lett. 110, 063003] processes are effective for the C_n ions only. Knowledge of the cooling rates of these ions are important for estimates of their formation and destruction rates in cold interstellar environments.
80.	Kjær, C., et al. (författare) Gas-phase Förster resonance energy transfer in mass-selected ions with methylene or peptide linkers between two dyes: a concerted dance of charges 2020 Ingår i: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 22:19, s. 11095-11100 Tidskriftsartikel (refereegranskat)abstract Förster Resonance Energy Transfer (FRET) between a photoexcited and a ground-state dye is dictated by how far apart the two dyes are compared to the Förster distance. While there is a significant number of studies on the process for biomacromolecules in solution, there are only a few reports on gas-phase FRET. Here we report on a simple gas-phase model system, synthesized with the rhodamine 575 (R575+) and rhodamine 640 (R640+) FRET pair and a covalent linker with four methylenes, R575+-(CH2)4-R640+. Each dye carries a positive charge which allows for mass-spectroscopy experiments. We have recorded gas-phase dispersed fluorescence spectra of the mass-selected dications excited at different wavelengths using the homebuilt LUNA (LUminescence iNstrument in Aarhus) setup and find in all cases that emission is exclusively from the R640+ acceptor dye. The linker does not interfere electronically with the dyes and simply acts as a spacer. We can therefore establish the direct effect of the interaction between the two dyes when it comes to emission band maximum. Indeed, we find that R640+ experiences a significant shift in its maximum from 560 ± 1 nm for the monomer cation to 577 ± 2 nm in the presence of R575+, independent of initial excitation of R575+ or R640+. This redshift is ascribed to the large polarizability along the long axis of the xanthene core structure, and that this polarizability is larger in the excited state than in the ground state. Experiments were also done on a triply charged 11-mer peptide labelled with the same two dyes, R575+-(Gly-Gln)5-Lys-R640+ + H+ (Gly = glycine, Gln = glutamine, and Lys = lysine) where the extra positive charge is located on the peptide. Again a redshifted emission spectrum of the donor is observed with maximum at 582 ± 2 nm. Our work clearly demonstrates strong sensitivity of the photophysics of one dye to the nearby environment, and that caution is needed when using the energy transfer efficiency to infer dye-dye separations in gas-phase experiments.
81.	Kjellberg, Mikael, 1980, et al. (författare) Femtosecond electron spectroscopy of coronene, benzo[GHI]perylene and anthracene 2010 Ingår i: Journal of Chemical Physics. - 0021-9606. ; 133:7 Tidskriftsartikel (refereegranskat)abstract The large polycyclic aromatic hydrocarbon molecules coronene, benzo[GHI]perylene, and anthracene have been ionized with femtosecond laser pulses at low laser intensities and the ionization process studied with velocity map imaging spectroscopy, supplemented with ion yield measurements. The electron spectra of coronene and benzo[GHI]perylene are structureless. Based on fluence and pulse duration dependence measurements, it is shown that the electron spectra are not produced in field ionization processes, and the ionization mechanism is identified to be a quasithermal statistical electron emission, previously suggested for the fullerenes C60 and C70. The anthracene photoelectron spectra are dominated by above threshold ionization features, but with some indication of quasithermal ionization at longer pulses.
82.	Kjellberg, Mikael, 1980, et al. (författare) Momentum map imaging photoelectron spectroscopy of fullerenes with femtosecond laser pulses 2010 Ingår i: Physical Review A. - 1050-2947. ; 81:2 Tidskriftsartikel (refereegranskat)abstract Photoelectron spectra of C60 and C70, ionized with ultrashort laser pulses, are measured with a momentum-map-imaging electron spectrometer. Above the photon energy, 1.6 eV, the spectra are essentially structureless and well described by Boltzmann distributions, with temperatures on the order of 104 K. This result is similar to previous results for C60 using a time-of-flight electron spectrometer, which are confirmed in this study. Comparisons of electron energy distributions recorded for identical laser intensities but for different pulse durations demonstrate unambiguously that a significant fraction of the electrons are emitted in quasithermal processes and results argue strongly against a field ionization or direct multiphoton ionization mechanism. For electron energies above the photon energy, which account for about half the intensity, the whole signal is consistent with this quasithermal emission.
83.	Kono, Naoko, et al. (författare) Electronic and vibrational radiative cooling of the small carbon clusters C4− and C6− 2018 Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 98:6 Tidskriftsartikel (refereegranskat)abstract Delayed electron detachment yields of C4− and C6− induced by photoexcitation in an electrostatic ion storage ring were measured as functions of excitation energies and laser firing times, allowing for a mapping of their radiative cooling in a wide energy range. The energy window concept and discrimination of one- and twophoton absorption are critical in understanding the obtained results. The experimentally obtained electronic and vibrational cooling rates were consistent with a simulation based on detailed-balance theory. The even-odd alternation of vibrational cooling rates, predicted from IR intensities, was also examined. We found that the larger anion cools faster, with no indication of an even-odd alternation.
84.	Kono, N., et al. (författare) Inverse internal conversion in C4- below the electron detachment threshold 2015 Ingår i: Physical Chemistry Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 17:38, s. 24732-24737 Tidskriftsartikel (refereegranskat)abstract Inverse internal conversion followed by recurrent fluorescence was observed as a fast decay (10 μs range) in the time profile of neutral yields from photo-excited C4- molecular ions. We also elucidated the contribution of such electronic radiative cooling to the C4- ions with internal energy far below the detachment threshold by an alternative novel approach, observing the laser wavelength and storage time dependence (ms range) of the total yield of the photo-induced neutrals.
85.	Kresin, Vitaly V., et al. (författare) Slow electron attachment as a probe of cluster evaporation processes 2011 Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 115, s. 6961-6972 Tidskriftsartikel (refereegranskat)abstract Neutral alkali clusters efficiently capture low-energy electrons with the aid of long-range polarization attraction. Upon attachment, the electron energy is dissipated into vibrations, heating the cluster and triggering evaporation of atoms and dimers. This process offers a novel means to explore nanocluster bonding and evaporation kinetics. The present work investigates the formation of . A crossed-beam experiment reveals that relative anion abundances become strongly and nontrivially restructured with respect to the neutral precursor beam. This restructuring is explained in quantitative detail by an analysis of evaporative cascades initiated by the attachment. The analysis thus furnishes a complete description of the electron attachment process, from initial attraction to final rearrangement of the cluster population. In addition, the paper describes a reconstruction of neutral cluster population in the supersonic beam, a new relation between the dissociation energies of cationic, neutral and anionic metal clusters, and a systematic derivation of cluster evaporation kinetics and internal temperature distributions.
86.	Lassesson, Andreas, 1976, et al. (författare) A femtosecond laser study of the endoral fullerenes Li@C60 and La@C82 2005 Ingår i: Eur. Phys. J. D. - : Springer Science and Business Media LLC. - 1434-6060. ; 34, s. 205-209 Tidskriftsartikel (refereegranskat)abstract The endohedral fullerenes La@C82 and Li@C60 have been studied in the gas phase with femtosecond laser excitation. The two molecules show qualitatively the same behaviour with respect to ion yield vs. pulse energy, but markedly different fragmentation patterns, with La@C82 fragmenting via the shrink-wrap mechanism and Li@C60 predominantly losing the metal atom in the first fragmentation step. The ion yields and electron energy distributions of La@C82 agree well with a recently developed model for fs laser ionisation of C60.
87.	Leidlmair, Christian, et al. (författare) Structures, Energetics, and Dynamics of Helium Adsorbed on Isolated Fullerene Ions 2012 Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 108:7 Tidskriftsartikel (refereegranskat)abstract Helium adsorbed on C60+ and C70+ exhibits phenomena akin to helium on graphite. Mass spectra suggest that commensurate layers form when all carbon hexagons and pentagons are occupied by one He each, but that the solvation shell does not close until 60 He atoms are adsorbed on C60+, or 62 on C70+. Molecular dynamics simulations of C60Hen+ at 4 K show that the commensurate phase is solid. Helium added to C60He32+ will displace some atoms from pentagonal sites, leading to coexistence of a registered layer of immobile atoms interlaced with a nonregistered layer of mobile atoms.
88.	Mamontov, Eugen, 1955, et al. (författare) Associations and dissociations with time-dependent reaction coefficients in finite polymer mixtures: The model and analytical-numerical method for solution by successive approximations 2017 Ingår i: Applied Mathematical Modelling. - : Elsevier BV. - 0307-904X. ; 51, s. 109-128 Tidskriftsartikel (refereegranskat)abstract The work deals with the association and dissociation reactions with time-dependent coef- ficients in finite mixtures of polymers dispersed in fluid media with solid components. The polymers are regarded to be formed by identical units, polymer-forming units (PFUs) and, thus, present homopolymers. The model takes into account the porosity of the dispersion- medium/polymer-mixture system. The work derives the model for the reactions in the fi- nite mixtures. The model presents a non-autonomous quadratic finite ODE system in a time-independent hyperplane and is based on the conservation law for the total num- ber of PFUs. A variety of engineering applications of the derived finite-mixture model are discussed. The simplest case of the finite mixtures, i.e., the monomer-dimer mix- tures with time-independent reaction coefficients is completely analyzed. An analytical- numerical (AN) method of the successive-approximations (SA) type is proposed for solv- ing the derived model. The AN/SA method includes explicit analytical expressions for each of the approximations in terms of the preceding approximation. The method is exact in the dissociation-only case. The approximations are expected to converge if the association- reaction coefficients are not too large and the zeroth approximations are not very far from the solution. The AN/SA method comprises two sequences of the approximations. If the first one converges uniformly in the entire time axis, then the limit function is a steady- state (or “dynamic equilibrium”) solution of the non-autonomous quadratic ODE system. The second sequence presumes that the first sequence is convergent in the above men- tioned sense. The second sequence is intended for calculation of the solutions of initial- value problems for the above ODE system in a semi-infinite time interval. The main differ- ences from common computational methods are formulated. The AN/SA method is quan- titatively illustrated with a few examples of the settings in the aforementioned case of monomer-dimer mixtures, also in comparison with the explicit Euler method. The form of the AN/SA method allows especially efficient implementation on multi-processor/multicore personal computers with graphic processing units even if the dimension of the state space is large. The developed model and method form a constructive framework for analysis or design of polymer mixtures dispersed in fluid-solid media. An application to prospective manufacturing of spatially heterogeneous polymer products is noted. A few directions for future research are proposed as well.
89.	Mehlig, Kirsten, 1964, et al. (författare) Energy distributions in multiple photon absorption experiments 2004 Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120, s. 4281-4288 Tidskriftsartikel (refereegranskat)abstract Photofragmentation experiments on molecules and clusters often involve multiple photon absorption. The distributions of the absorbed number of photons are frequently approximated by Poisson distributions. For realistic laser beam profiles, this approximation fails seriously due to the spatial variation of the mean number of absorbed photons across the laser beam. We calculate the distribution of absorbed energy for various laser and molecular-beam parameters. For a Gaussian laser beam, the spatially averaged distributions have a power-law behavior for low energy with a cutoff at an energy which is proportional to fluence. The power varies between –1 for an almost parallel laser beam and –5/2 for a divergent beam (on the scale of the molecular beam). We show that the experimental abundance spectra of fullerenes and small carbon clusters can be used to reconstruct the distribution of internal energy in the excited C60 molecule prior to fragmentation and find good agreement with the calculated curves
90.	Najafian, Kaveh, et al. (författare) Radiative cooling of C7- 2014 Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 140:10 Tidskriftsartikel (refereegranskat)abstract The spontaneous and photo-induced neutralization of C_7- produced in a laser ablation source was measured in an electrostatic storage ring. The measurements provide three independent determinations of the radiative cooling of the ions, based on the short time spontaneous decay and on the integrated amplitude and the shape of the photo-induced neutralization signal. The amplitude of the photo-induced signal was measured between 0.5 ms and 35 ms and found to depend on photon wavelength and ion storage time. All three signals can be reproduced with identical thermal IR radiative cooling rates with oscillator strengths equal to theoretical predictions. In addition, the measurements provide the excitation energy distribution.
91.	Partanen, Lauri, et al. (författare) Effect of Conformers on Free Energies of Atmospheric Complexes 2016 Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 120:43, s. 8613-8624 Tidskriftsartikel (refereegranskat)abstract In this article we show how to calculate free energies for atmospherically relevant complexes when multiple conformers and/or isomers are present. We explain why the thermal averaging methods used in several published works are incorrect. On the basis of our two sample cases, the sulfuric acid−pinic acid complex and the H2SO4)3(NH3)3(H2O)4 cluster, we provide numerical evidence that the use of these incorrect formulas can result in errors larger than 1 kcal/mol. We recommend that if vibrational frequencies and thus Gibbs free energies of the individual conformers are unavailable, one should not attempt to correct for the presence of multiple conformers and instead use only the global minimum conformers for both reactants and products. On the contrary, if the free energies for the conformers are calculated for both reactants and products, their effect can be accounted for by the statistical mechanical methods presented in this article.
92.	Podenok, S., et al. (författare) Electric field enhancement factors around a metallic, end-capped cylinder 2006 Ingår i: Nano. - 1793-2920. ; 1, s. 87-93 Tidskriftsartikel (refereegranskat)abstract We have calculated the electric field enhancement factor for a metallic cylinder with a hemispherical end-cap in a plane capacitor geometry paying particular attention to the dependence of the field enhancement factor on the anode distance. In addition, we have investigated the angular dependence of the local field at the end-cap. The numerical results, which cover a range of different ratios of cylinder lengths and anode distances, can be fitted with simple functional expressions which provide a useful scaling for calculations of field emission currents from closed cap carbon nanotubes or nanowires.
93.	Prasalovich, Sergei, 1976, et al. (författare) Surface entropy of rare-gas clusters 2005 Ingår i: J. Chem. Phys.. - : AIP Publishing. - 0021-9606. ; 123 Tidskriftsartikel (refereegranskat)abstract Abundances of Ar and Xe clusters produced in a supersonic expansion source are inverted to find relative dissociation energies. The values around the shell and subshell closings at N=55, 71, and 147 differ from theoretical values derived from ground-state energies of Lennard-Jones clusters. A significant part of the difference can be accounted for by the conformational entropies of surface atoms and vacancies.
94.	Rahinov, Igor, et al. (författare) Effect of a localized charge on the stability of Van der Waals clusters 2016 Ingår i: European Physical Journal D : Atomic, Molecular and Optical Physics. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 70:12 Tidskriftsartikel (refereegranskat)abstract The stability of anionic (SF6)N clusters (in the range of N < 23), generated in a supersonic expansion ion source with electron impact ionization, was investigated by measuring their blackbody induced radiative dissociation (BIRD) rates in an electrostatic ion beam trap (EIBT) at room temperature. The lifetime traces of EIBT-stored clusters were subjected to “master equation analysis” and the activation energies, Ea, for the evaporation of a SF6 monomer were extracted. We find that the decay rates of (SF6)N anionic clusters are larger than those of cationic SF5+ (SF6)N−1 measured previously by the same method, and their corresponding activation energies to be smaller. These observations provide further insight into the effect of localized charge on cluster stability.
95.	Rhind, Nicholas, et al. (författare) Comparative Functional Genomics of the Fission Yeasts 2011 Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 332:6032, s. 930-936 Tidskriftsartikel (refereegranskat)abstract The fission yeast clade-comprising Schizosaccharomyces pombe, S. octosporus, S. cryophilus, and S. japonicus-occupies the basal branch of Ascomycete fungi and is an important model of eukaryote biology. A comparative annotation of these genomes identified a near extinction of transposons and the associated innovation of transposon-free centromeres. Expression analysis established that meiotic genes are subject to antisense transcription during vegetative growth, which suggests a mechanism for their tight regulation. In addition, trans-acting regulators control new genes within the context of expanded functional modules for meiosis and stress response. Differences in gene content and regulation also explain why, unlike the budding yeast of Saccharomycotina, fission yeasts cannot use ethanol as a primary carbon source. These analyses elucidate the genome structure and gene regulation of fission yeast and provide tools for investigation across the Schizosaccharomyces clade.
96.	Ryding, Mauritz Johan, 1981, et al. (författare) X-ray induced fragmentation of size-selected salt cluster-ions stored in an ion trap 2014 Ingår i: RSC Advances. - 2046-2069. ; 4:88, s. 47743-47751 Tidskriftsartikel (refereegranskat)abstract A method for spectroscopic characterization of free ionic clusters and nanoparticles utilizing X-ray synchrotron radiation is presented. We demonstrate that size-selected ammonium bisulphate cluster ions, NH 4+(NH 4HSO4) n, captured in a linear ion trap, exhibit well-defined core-level absorption edges in the reconstructed fragment-ion abundance spectra. In addition to the specific photo-fragmentation pathways observed at the N1s-, O1s- and S2p-edges, dissociation also occurs as a consequence of clusters colliding with helium present as buffer gas in the ion trap. Separate off-beam experiments were conducted to establish the activation kinetics of these collision induced dissociation processes. Furthermore, it is demonstrated that the electrons released upon photoionization of background helium are too few in number to produce multiply charged cluster ions, and thereby induce fragmentation of the salt clusters, to any significant degree. The mechanisms for photon absorption and subsequent cluster fragmentation are analysed and discussed. In addition to its inherent element specificity, the method holds promise for cluster structure elucidation resulting from the sensitivity of the near edge absorption structure to the local chemical environment of the excited atom.
97.	Ryding, Mauritz J., et al. (författare) X-ray induced fragmentation of size-selected salt cluster-ions stored in an ion trap 2014 Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:88, s. 47743-47751 Tidskriftsartikel (refereegranskat)abstract A method for spectroscopic characterization of free ionic clusters and nanoparticles utilizing X-ray synchrotron radiation is presented. We demonstrate that size-selected ammonium bisulphate cluster ions, NH4+(NH4HSO4)(n), captured in a linear ion trap, exhibit well-defined core-level absorption edges in the reconstructed fragment-ion abundance spectra. In addition to the specific photo-fragmentation pathways observed at the N1s-, O1s- and S2p-edges, dissociation also occurs as a consequence of clusters colliding with helium present as buffer gas in the ion trap. Separate off-beam experiments were conducted to establish the activation kinetics of these collision induced dissociation processes. Furthermore, it is demonstrated that the electrons released upon photoionization of background helium are too few in number to produce multiply charged cluster ions, and thereby induce fragmentation of the salt clusters, to any significant degree. The mechanisms for photon absorption and subsequent cluster fragmentation are analysed and discussed. In addition to its inherent element specificity, the method holds promise for cluster structure elucidation resulting from the sensitivity of the near edge absorption structure to the local chemical environment of the excited atom.
98.	Schweikhard, L., et al. (författare) Cluster studies in ion traps 2005 Ingår i: Proceedings of ISACC 2003. - 1860944957 ; , s. 85-95 Konferensbidrag (övrigt vetenskapligt/konstnärligt)
99.	Schweikhard, L., et al. (författare) Photodissociation of Au30+ clusters stored in a Penning trap 2005 Ingår i: Eur. Phys. J. D. - : Springer Science and Business Media LLC. - 1434-6060. ; 36, s. 179-185 Tidskriftsartikel (refereegranskat)abstract Ion trapping allows detailed studies of atomic clusters with various interactions and over a large range of timescales. An overview of methods at hand is given and a specific example is presented in detail where size-selected Au30+ clusters have been stored in a Penning trap and photofragmented by exposure to the third harmonic of a Nd:YAG laser. The resulting mass spectra were sampled after reaction periods varying from 10μs to 1s. The data are used to extract relative dissociation energies, which agree well with model-free values determined previously by other means, albeit with a slightly larger magnitude of the odd-even effect. Below n≃24 the relative dissociation energies extracted from the abundance spectra develop very little over the five orders of magnitude in time covered in the experiments. This behavior has been predicted, but not tested previously. Above n≃24 both spectra and dissociation energies develop odd-even effects after a storage time of 10–100 ms. Possible reasons for this behavior are discussed.
100.	Shiromaru, H., et al. (författare) Cooling dynamics of carbon cluster anions 2015 Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 635 Tidskriftsartikel (refereegranskat)abstract A series of ion storage experiments on small carbon cluster anions was conducted to understand size-dependent cooling processes. The laser-induced delayed electron detachment time profile show clear even/odd alternation due to the presence of the electronic cooling. The time evolution of the internal energy distribution was simulated for Cn- (n=4 to 7) with a common procedure taking vibrational and electronic cooling into account.

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