PHOTOCHEMISTRY OF ADSORBED MOLECULES .8. PHOTODISSOCIATION, PHOTOELIMINATION, AND PHOTOREACTION IN VINYL-CHLORIDE ON LIF(001)

Photochemical processes that occur in submonolayers of vinyl chloride adsorbed on a single crystal of LiF have been investigated. Four different photofragments, Cl, C2H3, HCl, and C2H2, as well as intact parent molecules, C2H3Cl, were monitored by means of angularly resolved time-of-flight mass spectrometry following irradiation at 193 nm. The translational energy distributions of the fragments differ markedly from those observed in the gas phase. Cl atoms were formed through two photodissociation (PDIS) pathways at all surface coverages studied (< 2 monolayers), while HCl was formed by a unimolecular photoelimination (PEL) process at low coverages (<< 1 monolayer) and, in addition, by photoreaction (PRXN) in the adsorbed layer to yield more energetic HCl, at higher coverages (approximately 1 monolayer).