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Ionization and fragmentation of polycyclic aromatic hydrocarbon clusters in collisions with keV ions

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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Contributor : Jean-Yves Chesnel Connect in order to contact the contributor
Submitted on : Thursday, July 2, 2015 - 1:32:36 PM
Last modification on : Tuesday, October 4, 2022 - 4:00:27 PM



H. A. B. Johansson, H. Zettergren, A. I. S. Holm, F. Seitz, H. T. Schmidt, et al.. Ionization and fragmentation of polycyclic aromatic hydrocarbon clusters in collisions with keV ions. Physical Review A : Atomic, molecular, and optical physics, 2011, 84 (4), pp.043201. ⟨10.1103/PhysRevA.84.043201⟩. ⟨hal-01170849⟩



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