XUV excitation followed by ultrafast non-adiabatic relaxation in PAH molecules as a femto-astrochemistry experiment

Alexandre Marciniak (1) , V. Despre (1) , Thomas Barillot (1) , A. Rouzee (2) , M. C. E. Galbraith (2) , J. Klei (2) , C. -. H. Yang (2) , C. T. L. Smeenk (2) , Vincent Loriot (1) , S. Nagaprasad Reddy (3) , A. G. G. M. Tielens (4) , S. Mahapatra (3) , A. I. Kuleff (5) , M. J. J. Vrakking (2) , Franck Lepine (1)

1 ILM - Institut Lumière Matière [Villeurbanne]
2 Max-Born-institut, Berlin
3 School of Chemistry, University of Hyderabad
4 Leiden Observatory [Leiden]
5 PCI - Physikalisch-Chemisches Institut [Heidelberg]

Highly excited molecular species are at play in the chemistry of interstellar media and are involved in the creation of radiation damage in a biological tissue. Recently developed ultrashort extreme ultraviolet light sources offer the high excitation energies and ultrafast time-resolution required for probing the dynamics of highly excited molecular states on femtosecond (fs) (1 fs ¼ 10 À 15 s) and even attosecond (as) (1 as ¼ 10 À 18 s) timescales. Here we show that polycyclic aromatic hydrocarbons (PAHs) undergo ultrafast relaxation on a few tens of femtoseconds timescales, involving an interplay between the electronic and vibrational degrees of freedom. Our work reveals a general property of excited radical PAHs that can help to elucidate the assignment of diffuse interstellar absorption bands in astrochemistry, and provides a benchmark for the manner in which coupled electronic and nuclear dynamics determines reaction pathways in large molecules following extreme ultraviolet excitation.

Domaines: Chimie; Physique [physics]; Sciences de l'ingénieur [physics]

Alexandre Marciniak, V. Despre, Thomas Barillot, A. Rouzee, M. C. E. Galbraith, et al.. XUV excitation followed by ultrafast non-adiabatic relaxation in PAH molecules as a femto-astrochemistry experiment. Nature Communications, 2015, 6, pp.7909. ⟨10.1038/ncomms8909⟩. ⟨hal-02307271⟩