Regular Article

Hydrogenated pyrene: Statistical single-carbon loss below the knockout threshold^*

¹ Department of Physics, Stockholm University, Stockholm, 106 91, Sweden,
² Department of Physics and Astronomy, Aarhus University, 8000 Aarhus, Denmark

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Received: 29 December 2015
Received in final form: 29 February 2016
Published online: 14 April 2016

Abstract

An ongoing discussion revolves around the question of what effect hydrogenation has on carbon backbone fragmentation in polycyclic aromatic hydrocarbons (PAHs). In order to shed more light on this issue, we have measured absolute single carbon loss cross sections in collisions between native or hydrogenated pyrene cations (C₁₆H⁺_10+m, m = 0, 6, 16) and He as functions of center-of-mass energies down to 20 eV. Classical molecular dynamics (MD) simulations give further insight into energy transfer processes and also yield m-dependent threshold energies for prompt (femtoseconds) carbon knockout. Such fast, non-statistical fragmentation processes dominate CH_x-loss for native pyrene (m = 0), while much slower statistical fragmentation processes contribute significantly to single-carbon loss for the hydrogenated molecules (m = 6 and m = 16). The latter is shown by measurements of large CH_x-loss cross sections far below the MD knockout thresholds for C₁₆H⁺₁₆ and C₁₆H⁺₂₆.