TERT-BUTYL NITRITE SURFACE PHOTOCHEMISTRY - THE TRANSITION FROM SUBMONOLAYER TO MULTILAYER BEHAVIOR

The photochemistry of tert-butyl nitrite, (CH3)(3)CONO, adsorbed on Ag (111) at 355 nm has been studied using time-of-flight and reflection a dsorption infrared spectroscopy (RAIRS) for coverages ranging from 0.1 to 50 ML. For all coverages a thermal and hyperthermal NO desorption distribution is observed due to photodissociation. The thermal compone nt originates from hyperthermal NO molecules from the first and second layer, which were trapped by the silver substrate. The cross section for photodissociation is independent of coverage and matches the gas p hase value. This is consistent with a direct excitation into the S-1 s tate, For coverages exceeding 5 ML the outermost layers still dissocia te, but RAIRS shows that in the more inward layers caging is preventin g dissociation, Due to caging only isomerization of tert-butyl nitrite is allowed, as is evident from the RAIRS. (C) 1998 American Institute of Physics. [S0021-9606(98)01104-0].