The photodissociation of tert-butyl nitrite adsorbed on Ag(111): bimodal velocity distributions of the photoproducts

In this study the photodissociation of physisorbed tert-butyl nitrite, (CH3)3CONO, adsorbed on Ag(111) by 355 nm light is investigated at coverages between 0.15 and 50 layers at 85 K. Upon irradiation, time-of-flight spectroscopy showed desorbing NO molecules due to the photodissociation of the tert-butyl nitrite. These molecules show a bimodal velocity distribution with a thermal and a hyperthermal component at all the investigated coverages. The yield and the velocity of the hyperthermal component saturated at a coverage of 5 layers. The conclusion is made that if more than 5 layers are adsorbed the hyperthermal component is produced in the top 5 layers of the film via a direct excitation mechanism. The thermal component consisted of NO photoproducts which had equilibrated to the substrate temperature.