Control of H 2 Dissociative Ionization in the Nonlinear Regime Using Vacuum Ultraviolet Free-Electron Laser Pulses
Résumé
The role of the nuclear degrees of freedom in nonlinear two-photon single ionization of H2 molecules
interacting with short and intense vacuum ultraviolet pulses is investigated, both experimentally and
theoretically, by selecting single resonant vibronic intermediate neutral states. This high selectivity relies on
the narrow bandwidth and tunability of the pulses generated at the FERMI free-electron laser. A sustained
enhancement of dissociative ionization, which even exceeds nondissociative ionization, is observed and
controlled as one selects progressively higher vibronic states. With the help of ab initio calculations for
increasing pulse durations, the photoelectron and ion energy spectra obtained with velocity map imaging
allow us to identify new photoionization pathways. With pulses of the order of 100 fs, the experiment
probes a timescale that lies between that of ultrafast dynamical processes and that of steady state
excitations.
Origine | Fichiers éditeurs autorisés sur une archive ouverte |
---|