FEMTOSECOND VERSUS NANOSECOND SURFACE PHOTOCHEMISTRY - O2-K(CO ON PT(111) AT 80)

Desorption of O2 and production of CO2 from O2 coadsorbed with CO on P t(111) at 80 K were induced by laser pulses of femtosecond and nanosec ond durations. The photoyields with femtosecond pulses show highly non linear dependence on fluence, large enhancement of cross section, and increase of the O2 desorption to CO2 production branching ratio, when compared with desorption and reaction induced by nanosecond pulses. Th ese differences are attributed to multiple excitations occurring withi n the time scale of relaxation of the excited adsorbate-surface comple x, which are possible with high intensity femtosecond pulse laser irra diation.