Femtosecond Desorption Dynamics Probed by Time-Resolved Velocity Measurements

The velocity distribution of ${\mathrm{O}}_2$ photodesorbed from Pt(111) by femtosecond laser pulses is found to be approximately Maxwellian in form, with a translational temperature that increases with laser fluence. Time-resolved measurements using a two-pulse correlation scheme reveal a subpicosecond response in the translational temperature. These results are consistent with a desorption process driven by multiple electronic transitions, where the time-dependent substrate electronic temperature influences the velocity distribution of desorbing molecules.