The photodissociation dynamics of N 2O 4 multilayers adsorbed on a polycrystalline Au substrate at 80-140 K was investigated. The Au substrate was mainly composed of domains with (111) structure. Time-of-flight spectra of the photofragment 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 N 2O 4 adsorb on the Au substrate at 85 K were irradiated by the pulsed output of an excimer laser at λ = 193 and 351 nm. Photodissociation of the adlayers at 193 nm takes place by direct photoabsorption of N 2O 4. Since the top layers of N 2O 4 absorbed the UV light, superthermal NO and O photofragments are produced. Translationally and internally relaxed fragments are also produced from the photodissociation of the inner layers. At 351 nm, the bulk photoexcitation results in formation of slow NO photofragments. By comparing the effect of dissociation wavelengths, substrate temperatures and dose rates, it is shown that the photodissociation dynamics is governed by both the photoexcitation process and the adsorption state of N 2O 4 on the Au substrate.
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