PHOTO-STIMULATED DESORPTION OF NO FROM A PT(001) SURFACE

Desorption of NO molecules chemisorbed on a Pt(001) surface at 80 K induced by ultraviolet laser radiation is investigated by a resonance-enhanced multiphoton ionization technique. The desorption yield of neutral NO is proportional to pump laser fluence. which is indicative of a single-photon process. The translational, rotational, and vibrational temperatures of desorbed molecules are approximately 650, 300, and 1200 K, respectively. The substantial difference of these values from sample temperature implies that desorption is not thermally driven, but induced by electronic excitation. Polarization and wavelength dependences of a pump laser are examined to characterize the electronic excitation relevant to desorption. No significant difference is observed for either s- and p-polarization and at lambda = 193, 248, and 352 nm. The incidence angle dependence of the desorption yield is similar to that of the substrate ultraviolet light absorption. These results suggest that the initial step of photodesorption is substrate valence electron excitation.