CC BY 4.0 UnportedMarciniak, A.Despré, V.Barillot, T.Rouzée, A.Galbraith, M.C.E.Klei, J.Yang, C.-H.Smeenk, C.T.L.Loriot, V.Nagaprasad Reddy, S.Tielens, A.G.G.M.Mahapatra, S.Kuleff, A.I.Vrakking, M.J.J.Lépine, F.2022-07-292022-07-292015https://oa.tib.eu/renate/handle/123456789/9825http://dx.doi.org/10.34657/8863Highly 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=10−15s) and even attosecond (as) (1 as=10−18 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.enghttps://creativecommons.org/licenses/by/4.0/500polycyclic aromatic hydrocarbonabsorptionadiabaticitychemistryexcitationextreme ultravioletfemtoastrochemistrymoleculereaction analysisultraviolet radiationArticle