SURFACE FEMTOCHEMISTRY OF O-2 AND CO ON PT(111)

Desorption of O-2 and formation of CO2 were induced with subpicosecond laser pulses on a Pt(111) surface dosed with coadsorbed O-2 and CO. W e report the fluence dependent yields obtained over a range of laser w avelengths from 267 to 800 nm, and pulse durations from 80 fs to 3.6 p s. The nonlinear dependence of the yield on fluence is different at di fferent wavelengths. Two-pulse correlation measurements show two diffe rent time-scales relevant to the desorption. The results show that non thermalized electrons play a role in the surface chemistry, and that a n equilibrated pre-heating of the surface modes leads to enhanced deso rption.