학술논문
Time-resolved relaxation and fragmentation of polycyclic aromatic hydrocarbons investigated in the ultrafast XUV-IR regime
Document Type
Author
Lee, J. W.L.; Tikhonov, D. S.; Chopra, P.; Maclot, S.; Steber, A. L.; Gruet, S.; Allum, F.; Boll, R.; Cheng, X.; Düsterer, S.; Erk, B.; Garg, D.; He, L.; Heathcote, D.; Johny, M.; Kazemi, M. M.; Köckert, H.; Lahl, J.; Lemmens, A. K.; Loru, D.; Mason, R.; Müller, E.; Mullins, T.; Olshin, P.; Passow, C.; Peschel, J.; Ramm, D.; Rompotis, D.; Schirmel, N.; Trippel, S.; Wiese, J.; Ziaee, F.; Bari, S.; Burt, M.; Küpper, J.; Rijs, A. M.; Rolles, D.; Techert, S.; Eng-Johnsson, P.; Brouard, M.; Vallance, C.; Manschwetus, B.; Schnell, M.
Source
Nature Communications. 12(1)
Subject
Language
English
ISSN
2041-1723
Abstract
Polycyclic aromatic hydrocarbons (PAHs) play an important role in interstellar chemistry and are subject to high energy photons that can induce excitation, ionization, and fragmentation. Previous studies have demonstrated electronic relaxation of parent PAH monocations over 10–100 femtoseconds as a result of beyond-Born-Oppenheimer coupling between the electronic and nuclear dynamics. Here, we investigate three PAH molecules: fluorene, phenanthrene, and pyrene, using ultrafast XUV and IR laser pulses. Simultaneous measurements of the ion yields, ion momenta, and electron momenta as a function of laser pulse delay allow a detailed insight into the various molecular processes. We report relaxation times for the electronically excited PAH*, PAH+* and PAH2+* states, and show the time-dependent conversion between fragmentation pathways. Additionally, using recoil-frame covariance analysis between ion images, we demonstrate that the dissociation of the PAH2+ ions favors reaction pathways involving two-body breakup and/or loss of neutral fragments totaling an even number of carbon atoms.