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- Tomita, S., et al.
(författare)
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Lifetimes of C602- and C702- dianions in a storage ring
- 2006
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Ingår i: J. Chem. Phys.. - : AIP Publishing. - 0021-9606. ; 124
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Ions Colliding with Cold Polycyclic Aromatic Hydrocarbon Clusters
- 2010
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 105:21, s. 213401-
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Johansson, Henrik A. B., et al.
(författare)
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Ionization and fragmentation of polycyclic aromatic hydrocarbon clusters in collisions with keV ions
- 2011
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 84:4, s. 043201-
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Multiple ionization and fragmentation of isolated pyrene and coronene molecules in collision with ions
- 2011
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 83:2, s. 022704-
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Liu, B., et al.
(författare)
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Electron capture induced dissociation of nucleotide anions in water nanodroplets
- 2008
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:7, s. 075102-
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Low energy ions interacting with anthracene molecules and clusters
- 2012
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 279, s. 140-143
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Tidskriftsartikel (refereegranskat)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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