Photodissociation of N2O4 multilayer adsorbed on a polycrystalline Au substrate

The photodissociation dynamics of N2O4 multilayers adsorbed on a polycrysta lline Au substrate at 80-140 K was investigated. The Au substrate was mainl y composed of domains with (111) structure. Time-of-Right spectra of the ph otofragment NO and O as well as infrared reflection absorption spectra for the surface adsorbed species on the Au substrate were measured. Typically, four to five monolayers of N2O4 adsorb on the Au substrate at 85 K were irr adiated by the pulsed output of an excimer laser at lambda = 193 and 351 nm . Photodissociation of the adlayers at 193 nm takes place by direct photoab sorption of N2O4. Since the top layers of N2O4 absorbed the UV light, super thermal NO and O photofragments are produced. Translationally and internall y relaxed fragments are also produced from the photodissociation of the inn er layers. At 351 nm, the bulk photoexcitation results in formation of slow NO photofragments. By comparing the effect of dissociation wavelengths, su bstrate temperatures and dose rates, it is shown that the photodissociation dynamics is governed by both the photoexcitation process and the adsorptio n state of N2O4 on the Au substrate.