| 1. |
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| 2. |
- 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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| 3. |
- Kadhane, U., et al.
(author)
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Near-infrared photoabsorption by C-60 dianions in a storage ring
- 2009
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131:1
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Journal article (peer-reviewed)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.
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| 4. |
- Seitz, Fabian, et al.
(author)
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Ions colliding with clusters of fullerenes-Decay pathways and covalent bond formations
- 2013
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 139:3
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Journal article (peer-reviewed)abstract
- We report experimental results for the ionization and fragmentation of weakly bound van der Waals clusters of n C-60 molecules following collisions with Ar2+, He2+, and Xe20+ at laboratory kinetic energies of 13 keV, 22.5 keV, and 300 keV, respectively. Intact singly charged C-60 monomers are the dominant reaction products in all three cases and this is accounted for by means of Monte Carlo calculations of energy transfer processes and a simple Arrhenius-type [C-60](n)(+) -> C-60(+) + (n - 1)C-60 evaporation model. Excitation energies in the range of only similar to 0.7 eV per C-60 molecule in a [C-60](13)(+) cluster are sufficient for complete evaporation and such low energies correspond to ion trajectories far outside the clusters. Still we observe singly and even doubly charged intact cluster ions which stem from even more distant collisions. For penetrating collisions the clusters become multiply charged and some of the individual molecules may be promptly fragmented in direct knock-out processes leading to efficient formations of new covalent systems. For Ar2+ and He2+ collisions, we observe very efficient C-119(+) and C-118(+) formation and molecular dynamics simulations suggest that they are covalent dumb-bell systems due to bonding between C-59(+) or C-58(+) and C-60 during cluster fragmentation. In the Ar2+ case, it is possible to form even smaller C-120-2m(+) molecules (m = 2-7), while no molecular fusion reactions are observed for the present Xe20+ collisions.
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| 5. |
- Zettergren, Henning, et al.
(author)
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Bond formation in C-59(+)-C-60 collisions
- 2014
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In: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : Institute of Physics (IOP).
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Conference paper (peer-reviewed)abstract
- In this work, we show that keV-ions are able to remove single carbon atoms from individual fullerenes in clusters of C-60 molecules. This very efficiently leads to the formation of exotic q dumbbell molecules through secondary C-59(+) - C-60 collisions within the fragmenting cluster. Such molecular fusion processes are inherently different from those induced by photons where only products with even numbers of carbon atoms are observed. Thus, ion collisions ignite unique and hitherto overlooked secondary reactions in small aggregates of matter. This relates to the question on how complex molecules may form in e.g. space.
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| 6. |
- Zettergren, Henning, et al.
(author)
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Formation of dumb-bell C118 and C119 inside clusters of C60 -molecules
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Journal article (peer-reviewed)abstract
- We report highly selective covalent bond-modifications in collisions between keV alpha particles and van der Waals clusters of C60-fullerenes. Surprisingly, C119+ and C118+ are the dominant molecular fusion products. We use Molecular Dynamics simulations to show that C59+ and C58+ ions - effectively produced in prompt knock-out processes with He2+ - react rapidly with C60 to form dumb-bell C119+ and C118+ . Ion impact on molecular clusters in general is expected to lead to efficient secondary reactions of interest for astrophysics. These reactions are different from those induced by photons.
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| 7. |
- Zettergren, Henning, et al.
(author)
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Formations of Dumbbell C-118 and C-119 inside Clusters of C-60 Molecules by Collision with alpha Particles
- 2013
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 110:18
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Journal article (peer-reviewed)abstract
- We report highly selective covalent bond modifications in collisions between keV alpha particles and van der Waals clusters of C-60 fullerenes. Surprisingly, C-119(+) and C-118(+) are the dominant molecular fusion products. We use molecular dynamics simulations to show that C-59(+) and C-58(+) ions-effectively produced in prompt knockout processes with He2+-react rapidly with C-60 to form dumbbell C-119(+) and C-118(+). Ion impact on molecular clusters in general is expected to lead to efficient secondary reactions of interest for astrophysics. These reactions are different from those induced by photons.
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| 8. |
- 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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| 9. |
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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. |
- Tomita, S., et al.
(author)
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Dynamic Jahn-Teller effects in isolated C60- studied by near-infrared spectroscopy in a storage ring
- 2005
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In: Phys. Rev. Lett.. - 0031-9007. ; 94
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Journal article (peer-reviewed)abstract
- We have measured the near-infrared absorption spectrum for isolated C ions at room temperature. Two bands, at 9145 cm-1 and 10460 cm-1, have been identified in addition to the main absorption band at 9382 cm-1, seen also at low temperature in a matrix. An interpretation based on the theory of dynamic Jahn-Teller effects is proposed.
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| 12. |
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| 13. |
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| 14. |
- 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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| 15. |
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| 16. |
- 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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| 17. |
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| 18. |
- 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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| 19. |
- 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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| 20. |
- 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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| 21. |
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| 22. |
- 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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