title: Ultrafast dynamics of photoionized acetylene.
abstract: Acetylene cations [HCCH](+) produced in the A(2)Σ(g)(+) state by extreme ultraviolet (XUV) photoionization are investigated theoretically, based on a mixed quantum-classical approach. We show that the decay of the A(2)Σ(g)(+) state occurs via both ultrafast isomerization and nonradiative electronic relaxation. We find a time scale for hydrogen migration and electronic decay of about 60 fs, in good agreement with recent XUV-pump/XUV-probe time-resolved experiments on the same system [Phys. Rev. Lett. 105, 263002 (2010)]. Moreover, we predict an efficient vibrational energy redistribution mechanism that quickly transfers excess energy from the isomerization coordinates to slower modes in a few hundred femtoseconds, leading to a partial regeneration of acetylenelike conformations.
authors.affiliation: Center for Free-Electron Laser Science, DESY, Notkestrasse 85, D-22607 Hamburg, Germany.
authors.forename: Mohamed El-Amine
authors.initials: Mel-A
authors.lastname: Madjet
authors.forename: Oriol
authors.initials: O
authors.lastname: Vendrell
authors.forename: Robin
authors.initials: R
authors.lastname: Santra