STATE-RESOLVED STUDY OF COADSORPTION EFFECTS ON THE STIMULATED DISSOCIATION OF NO2 ON PT(111)

Stimulated surface processes, which are induced by electronic transitions, are especially sensitive to the presence of coadsorbates. We present here a detailed study of electron (5-350 eV) stimulated dissociation of chemisorbed NO2 on an O-covered Pt(111) surface, utilizing state-resolved laser resonance-ionization detection of the NO gas-phase product. Several dramatic effects on NO2 dissociation occur with increasing O atom coverage (up to theta-o = 0.75 monolayer). First there is a large (x 26) enhancement in the specific dissociation yield. Second, there is a narrowing of the translational energy distributions. A third observation is a distinct propensity (> 4:1 at low J) for populating the upper (OMEGA = 3/2) over the lower (OMEGA = 1/2) level of the spin-orbit-split No 2-PI-OMEGA ground state. The enhanced yield can be understood in terms of increased lifetime(s) due to an O-induced reduction in charge transfer screening. Diminished charge transfer also reduces the vibrational and rotational excitation of the NO product. The spin-orbit propensity might arise from substrate reneutralization of NO+ following Auger decay of the primary excitation.