EFFECTS OF VIBRATIONAL-EXCITATION IN PHOTOSTIMULATED DESORPTION

Excitation of vibrational and rotational degrees of freedom, which occ urs in the desorption process of NO and CO molecules from Pt(111) and Pt(001) surfaces with ultraviolet nanosecond-pulsed laser irradiation, is investigated by resonance-enhanced multiphoton ionization detectio n. Desorbed NO molecules are highly excited in vibration and rotation, whereas CO desorbed from Pt is rotationally cold and vibrationally ex cited. On the basis of the substrate-mediated desorption mechanism, th e population in the first vibrational excited state and the rotational energy distribution can be consistently interpreted. In particular, w e propose a simple scheme interpreting the rotational energy distribut ion.