VIBRATIONALLY ASSISTED ELECTRONIC DESORPTION - FEMTOSECOND SURFACE-CHEMISTRY OF O2 PD(111)/

The process of desorption for the system Of 02/Pd (111) under excitati on by 100 fs pulses of visible light has been examined. Molecular deso rption is found to occur with high efficiency and a nonlinear dependen ce on laser fluence. Direct time-domain measurements using a two-pulse correlation scheme reveal a dominant subpicosecond response together with a weaker, but significant correlation persisting for tens of pico seconds. These results imply a desorption process driven by the high e lectron temperatures produced by the femtosecond laser radiation. The slower component of the correlation response is interpreted as an enha ncement of the desorption rate by adsorbate vibrational excitation.