Using laser resonance-enhanced ionisation spectroscopy, we have studied electron (6-350 eV) stimulated dissociation of NO2 coadsorbed with up to 0.75 monolayer of atomic O on Pt(111). Several dramatic effects on NO2 dissociation occur due to the presence of O. There is a large ( × 26) enhancement in the specific dissociation yield, a narrowing of the NO translational energy distributions, and a distinct propensity ( > 4:1 at low J) for populating the upper Ω = 3 2 NO spin-orbit level over the Ω = 1 2 level. The spin-orbit state distribution of the O(3PJ) dissociation fragment is (5.0): (2.5): (1.0) for J = 2, 1 and 0, which is within experimental error of the statistical (T → ∞) 2J + 1 limit. The enhanced yield probably results from an increased excited state lifetime due to a reduction in substrate charge-transfer screening. We have also detected O(3PJ = 2,1,0) and NO X2 Π 3 2, 1 2(v = 5) above an electron (6-350 eV) beam irradiated Pt(111) surface containing coadsorbed O2 and NO at 90 K. We conclude that both O(3PJ) and NO(v = 5) are laser-induced photodissociation fragments of NO2 desorbates. The NO2 is probably the reaction product of a collision between an O atom (created by electron-stimulated dissociation of adsorbed O2) and an NO(a). We correlate the 10 eV NO2 production threshold with the dissociative ionization of the 3σg molecular bonding orbital of O2(a).
ASJC Scopus subject areas
- Nuclear and High Energy Physics