| 1. |
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| 2. |
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| 3. |
- Tomita, S., et al.
(author)
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Lifetimes of C602- and C702- dianions in a storage ring
- 2006
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In: J. Chem. Phys.. - : AIP Publishing. - 0021-9606. ; 124
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Journal article (peer-reviewed)abstract
- C602- and C702- dianions have been produced by electrospray of the monoanions and subsequent electron pickup in a Na vapor cell. The dianions were stored in an electrostatic ring and their decay by electron emission was measured up to 1 s after injection. While C ions are stable on this time scale, except for a small fraction of the ions which have been excited by gas collisions, most of the C ions decay on a millisecond time scale, with a lifetime depending strongly on their internal temperature. The results can be modeled as decay by electron tunneling through a Coulomb barrier, mainly from thermally populated triplet states about 120 meV above a singlet ground state. At times longer than about 100 ms, the absorption of blackbody radiation plays an important role for the decay of initially cold ions. The tunneling rates obtained from the modeling, combined with WKB estimates of the barrier penetration, give a ground-state energy 200±30 meV above the energy of the monoanion plus a free electron and a ground-state lifetime of the order of 20 s.
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| 4. |
- Holm, Anne I. S., et al.
(author)
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Ions Colliding with Cold Polycyclic Aromatic Hydrocarbon Clusters
- 2010
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 105:21, s. 213401-
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Journal article (peer-reviewed)abstract
- We report the first experimental study of ions interacting with clusters of polycyclic aromatic hydrocarbon (PAH) molecules. Collisions between 11.25 keV He-3(+) or 360 keV Xe-129(20+) and weakly bound clusters of one of the smallest PAH molecules, anthracene, show that C14H10 clusters have much higher tendencies to fragment in ion collisions than other weakly bound clusters. The ionization is dominated by peripheral collisions in which the clusters, very surprisingly, are more strongly heated by Xe20+ collisions than by He+ collisions. The appearance size is k = 15 for [C14H10](k)(2+).
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| 5. |
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| 6. |
- Johansson, Henrik A. B., et al.
(author)
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Ionization and fragmentation of polycyclic aromatic hydrocarbon clusters in collisions with keV ions
- 2011
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 84:4, s. 043201-
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Journal article (peer-reviewed)abstract
- We report on an experimental study of the ionization and fragmentation of clusters of k polycyclic aromatic hydrocarbon (PAH) molecules using anthracene, C14H10, or coronene, C24H12. These PAH clusters are moderately charged and strongly heated in small impact parameter collisions with 22.5-keV He2+ ions, after which they mostly decay in long monomer evaporation sequences with singly charged and comparatively cold monomers as dominating end products. We describe a simple cluster evaporation model and estimate the number of PAH molecules in the clusters that have to be hit by He2+ projectiles for such complete cluster evaporations to occur. Highly charged and initially cold clusters are efficiently formed in collisions with 360-keV Xe20+ ions, leading to cluster Coulomb explosions and several hot charged fragments, which again predominantly yield singly charged, but much hotter, monomer ions than the He2+ collisions. We present a simple formula, based on density-functional-theory calculations, for the ionization energy sequences as functions of coronene cluster size, rationalized in terms of the classic electrostatic expression for the ionization of a charged conducting object. Our analysis indicates that multiple electron removal by highly charged ions from a cluster of PAH molecules rapidly may become more important than single ionization as the cluster size k increases and that this is the main reason for the unexpectedly strong heating in these types of collisions.
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| 7. |
- Lawicki, A., et al.
(author)
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Multiple ionization and fragmentation of isolated pyrene and coronene molecules in collision with ions
- 2011
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 83:2, s. 022704-
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Journal article (peer-reviewed)abstract
- The interaction of multiply charged ions (He2+, O3+, and Xe20+) with gas-phase pericondensed polycyclic aromatic hydrocarbon (PAH) molecules of coronene (C24H12) and pyrene (C16H10) is studied for low-velocity collisions (v <= 0.6 a.u.). The mass spectrometric analysis shows that singly and up to quadruply charged intact molecules are important reaction products. The relative experimental yields are compared with the results of a simple classical over-the-barrier model. For higher molecular charge states, the experimental yields decrease much more strongly than the model predictions due to the instabilities of the multiply charged PAH molecules. Even-odd oscillations with the number of carbon atoms, n, in the intensity distributions of the CnHx+ fragments indicate a linear chain structure of the fragments similar to those observed for ion-C60 collisions. The latter oscillations are known to be due to dissociation energy differences between even-and odd-n Cn-chain molecules. For PAH molecules, the average numbers of H atoms attached to the CnHx chains are larger for even-n reflecting acetylenic bond systems.
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| 8. |
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| 9. |
- Liu, B., et al.
(author)
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Electron capture induced dissociation of nucleotide anions in water nanodroplets
- 2008
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:7, s. 075102-
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Journal article (peer-reviewed)abstract
- We have studied the outcome of collisions between the hydrated nucleotide anion adenosine 5′-monophosphate (AMP) and sodium. Electron capture leads to hydrogen loss as well as water evaporation regardless of the initial number m of water molecules attached to the parent ion (m ⩽ 16). The yield of dianions with microsecond lifetimes increases strongly with m, which is explained from dielectric screening of the two charges by the water nanodroplet. For comparison, collision induced dissociation results in water losses with no or very little damage of the AMP molecule itself.
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| 10. |
- Rousseau, P., et al.
(author)
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Low energy ions interacting with anthracene molecules and clusters
- 2012
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 279, s. 140-143
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Journal article (peer-reviewed)abstract
- The interaction of slow ions (nu similar to 0.4 au.) with a small polycyclic aromatic hydrocarbon, namely anthracene (C14H10), is studied in the gas-phase either with the isolated molecule or with a pure cluster target. We discuss the ionization and fragmentation of the molecule with respect to the projectile charge state, i.e. for singly charged He+ ions and for multiply charged Xe20+. ions. For the isolated C14H10, single or multiple ionization of the molecule occurs under ion impact. The (multi) cation relative yields are compared with those obtained by other ionization methods (electron and fs-laser). The molecular dissociation occurs by loss of hydrogen and small hydrocarbon molecules, leading to the formation of CnHx cations. The interaction of Xe20+ with C14H10 clusters gives surprising results, i.e. the emission of hotter monomer compared to the interaction with He+.
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| 11. |
- Seitz, Fabian, 1980-, et al.
(author)
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Polycyclic aromatic hydrocarbon-isomer fragmentation pathways : Case study for pyrene and fluoranthene molecules and clusters
- 2011
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 135:6, s. 064302-
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Journal article (peer-reviewed)abstract
- We report on measurements of the ionization and fragmentation of polycyclic aromatic hydrocarbon (PAH) targets in Xe(20+) + C(16)H(10) and Xe(20+) + [C(16)H(10)](k) collisions and compare results for the two C(16)H(10) isomers: pyrene and fluoranthene. For both types of targets, i.e., for single PAH molecules isolated in vacuum or for isomerically pure clusters of one of the molecules, the resulting fragment spectra are surprisingly similar. However, we do observe weak but significant isomer effects. Although these are manifested in very different ways for the monomer and cluster targets, they both have at their roots small differences (<2.5 eV) between the total binding energies of neutral, and singly and multiply charged pyrene and fluoranthene monomers. The results will be discussed in view of the density functional theory calculations of ionization and dissociation energies for fluoranthene and pyrene. A simple classical over-the-barrier model is used to estimate cross sections for single-and multiple-electron transfer between PAHs and ions. Calculated single and multiple ionization energies, and the corresponding model PAH ionization cross sections, are given.
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| 12. |
- Zettergren, Henning, et al.
(author)
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Fragmentation and ionization of C70 and C60 by slow ions of intermediate charge
- 2006
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In: European Physical Journal D. - : Springer. - 1434-6060 .- 1434-6079. ; 38:2, s. 299-306
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Journal article (peer-reviewed)abstract
- We have measured total and coincident (with outgoing charge-state analyzed projectiles) ionization and fragmentation spectra of C 60 and C70 following collisions with Xe4+ and Kr4+ at v = 0. 06 a.u. Intact positive fullerene ions in charge states up to five (C 5+ 60 and C 5+ 70 ) are produced with both projectiles and for Kr 4++C70 collisions we even observe a small C 6+ 70 peak. The C 3+ 60 /70−2m (m = 1–7) intensity distributions are predominantly associated with the stabilization of three electrons on the projectile ( s = 3) and are significantly different for Xe 4+- and Kr4+ -projectiles. On the other hand, we find remarkable similarities in the C + 3 -C + 11 multi-fragmentation pattern regardless of projectile species (mass) although they are associated with closer encounters in which the projectile is fully neutralized ( s = 4). Simple Monte Carlo calculations of nuclear and electronic loss processes show that both these contributions are very similar in glancing Xe 4++C60 and Kr4++C60 collisions, suggesting that frontal (and more violent) collisions are strongly suppressed under the present experimental conditions. Nevertheless it is surprising that the more distant collisions ( s = 3) are projectile mass dependent, while the closer collisions (s = 4) are not. This indicates that this simple approach (although it reproduces more advanced quantum mechanical calculations for slow collisions with singly charged atomic ions rather well) is not valid for a comprehensive description of the energy transfer processes in the present collision systems involving projectiles of higher charge states.
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| 13. |
- Zettergren, Henning, et al.
(author)
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Magic and hot giant fullerenes formed inside ion irradiated weakly bound C-60 clusters
- 2010
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:10, s. 104301-
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Journal article (peer-reviewed)abstract
- We find that the most stable fullerene isomers, C-70-C-94, form efficiently in close-to central collisions between keV atomic ions and weakly bound clusters of more than 15 C-60-molecules. We observe extraordinarily high yields of C-70 and marked preferences for C-78 and C-84. Larger even-size carbon molecules, C-96-C-180, follow a smooth log-normal (statistical) intensity distribution. Measurements of kinetic energies indicate that C-70-C-94 mainly are formed by coalescence reactions between small carbon molecules and Coo, while C-n with n >= 96 are due to self-assembly (of small molecules) and shrinking hot giant fullerenes.
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| 14. |
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| 15. |
- Gatchell, Michael, et al.
(author)
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Ions colliding with polycyclic aromatic hydrocarbon clusters
- 2013
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In: Physica Scripta. - 0031-8949 .- 1402-4896. ; T156, s. 014062-
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Journal article (peer-reviewed)abstract
- We have measured the ionization and fragmentation of polycyclic aromatic hydrocarbon (PAH) molecules and their clusters. We find that PAH clusters containing up to roughly 100 individual molecules fragment strongly following collisions with keV ions in low or high charge states (q). For both types of collisions, singly charged PAH molecules are found to be the dominant products but for very different reasons. A high-q ion projectile charge leads to strong multiple ionization of the PAH clusters and subsequent Coulomb explosions. A low-q ion projectile charge often leads to single ionization but stronger internal heating and long evaporation sequences with a singly charged PAH monomer as the end product. We have developed a Monte Carlo method for collision-induced heating of PAH clusters and present an evaporation model where the clusters cool slowly as most of the internal energies are stored in intramolecular vibrations and not in molecule-molecule vibrations.
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| 16. |
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| 17. |
- Maisonny, R., et al.
(author)
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Highly Charged Ion : Induced Water Cluster Fragmentation
- 2012
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In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:10, s. 102053-
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Journal article (peer-reviewed)abstract
- Interaction between slow multiply charged ions and small to medium-size neutral water clusters is investigated. Strong projectile charge dependence is found for all of the fragmentation patterns. A variation of the projectile charge dramatically changes the proportion of multi-electron removal, the fragment kinetic energies as well as the mean size of the emitted fragments. First results for highly charged ion - water cluster ion collisions will also be presented.
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| 18. |
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| 19. |
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| 20. |
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| 21. |
- Zettergren, H., et al.
(author)
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Even-odd effects in the ionization cross sections of [C60]2 and [C60C70] dimers
- 2007
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 75:5, s. 051201-
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Journal article (peer-reviewed)abstract
- We report strong even-odd effects in multiple ionization yields of van der Waals dimers in slowXe30+ + ͓C60͔2͓͑C60C70͔͒ → ̄ + ͓C60͔2r+͓͑C60C70͔r+͒ electron-transfer collisions as functions of r Յ 7. Thisbehavior may be due to even-odd variations in the sequences of dimer ionization energies as calculated with anelectrostatic model including an electrical fullerene-fullerene contact at the 19a0 center-center separation in͓C60͔2+. Prompt dissociations predominantly yield intact fullerenes ͓C60͔2r+ → C60r1+ + C60r2+ in the same͑r1 = r2, even r͒ or nearby ͑r1 = r2 ± 1, odd r Ͼ 1͒ charge states.
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| 22. |
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| 23. |
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| 24. |
- Zettergren, H., et al.
(author)
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Stabilities of multiply charged dimers and clusters of fullerenes
- 2007
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:22, s. 224303-
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Journal article (peer-reviewed)abstract
- The authors find even-odd variations as functions of r (...+[C60]2(r+)([C60C70](r+)) electron-transfer collisions. This even-odd behavior is in sharp contrast to the smooth one for fullerene monomers and may be related to even-odd effects in dimer ionization energies in agreement with results from an electrostatic model. The kinetic energy releases for dimer dissociations [predominantly yielding intact fullerenes [C60]2(r+)-->C60(r1+)+C60(r2+) in the same (r1=r2) or nearby (r1=r2+/-1) charge states] are found to be low in comparison with the corresponding model results indicating that internal excitations of the separating (intact) fullerenes are important. Experimental appearance sizes for the heavier clusters of fullerenes [C60]n(r+) (n>3 and r=2-5) compare well with predictions from a new nearest-neighbor model assuming that r unit charges in [C60]n(r+) are localized to r C60 molecules such that the Coulomb energy of the system is minimized. The system is then taken to be stable if (i) two (singly) charged C60 are not nearest neighbors and (ii) the r C60(+) molecules have binding energies to their neutral nearest neighbors which are larger than the repulsive energies for the (r-1) C60(+)-C60(+) pairs. Essential ingredients in the nearest-neighbor model are cluster geometries and the present results on dimer stabilities.
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| 25. |
- Haag, Nicole, et al.
(author)
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Collisions with biomolecules embedded in smallwater clusters
- 2009
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Conference paper (peer-reviewed)abstract
- We have studied fragmentation of water embedded adenosine 5’-monophosphate(AMP) anions after collisions with neutral sodium atoms. At a collision energy of 50 keV,loss of water molecules from the collisionally excited cluster ions is the dominant process andfragmentation of the AMP itself is almost completely prohibited if the number of attachedwater molecules is larger than 13. However, regardless of the initial number of water moleculesattached to the ion, capture of an electron, i.e. formation of a dianion, always leads to loss ofa single hydrogen atom accompanied by evaporation of water molecules. This damaging effectbecomes more important as the size of the water cluster increases, which is just the oppositeto the protective behavior observed for collision induced dissociation (CID) without electrontransfer. For both cases, the loss of water molecules within the experimental time frame isqualitatively well described by means of a common model of an evaporative ensemble. Thesesimulations, however, indicate that characteristically different distributions of internal energyare involved in CID and electron capture induced dissociation.
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| 26. |
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| 27. |
- Zettergren, Henning, et al.
(author)
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Electron-Capture-Induced Dissociation of Microsolvated Di- and > Tripeptide Monocations : Elucidation of Fragmentation Channels from > Measurements of Negative Ions
- 2009
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In: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 10:9-10, s. 1619-1623
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Journal article (peer-reviewed)abstract
- The branching ratio between ammonia loss and NCα bond cleavage of singly charged microsolvated peptides after electron capture from cesium depends on the solvent molecule attached. Density functional calculations reveal that for [GA+H]+(CE) (G=glycine, A=alanine, CE=crown ether), the singly occupied molecular orbital of the neutral radical is located mainly on the amide group (see picture). The results from an experimental study of bare and microsolvated peptide monocations in high-energy collisions with cesium vapor are reported. Neutral radicals form after electron capture from cesium, which decay by H loss, NH3 loss, or NCα bond cleavage into characteristic z. and c fragments. The neutral fragments are converted into negatively charged species in a second collision with cesium and are identified by means of mass spectrometry. For protonated GA (G=glycine, A=alanine), the branching ratio between NH3 loss and NCα bond cleavage is found to strongly depend on the molecule attached (H2O, CH3CN, CH3OH, and 18-crown-6 ether (CE)). Addition of H2O and CH3OH increases this ratio whereas CH3CN and CE decrease it. For protonated AAA ([AAA+H]+), a similar effect is observed with methanol, while the ratio between the z1 and z2 fragment peaks remains unchanged for the bare and microsolvated species. Density functional theory calculations reveal that in the case of [GA+H]+(CE), the singly occupied molecular orbital is located mainly on the amide group in accordance with the experimental results.
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