THE PHOTOCHEMISTRY OF CD3I ADSORBED ON THE TIO2(110) SURFACE

The photochemistry of CD3I adsorbed on the TiO2(110) surface at simila r to 100 K has been investigated at 257, 275, and 302 mn using modulat ed continuous-wave laser irradiation followed by resonantly enhanced m ultiphoton ionization of fragments expelled from the adsorbate layer. Photodissociation at these wavelengths produces methyl radicals by dir ect photolysis of those methyl iodide adsorbate molecules located at t he vacuum-surface interface. The photodissociation dynamics is altered from the gas phase. Methyl radicals with velocities comparable to tho se observed in gas phase dissociation are detected with a narrow angul ar distribution consistent with a preferential alignment of the C-I bo nd along the surface normal. The I/I branching ratio of these high ve locity species is altered toward production of ground state iodine com pared to the gas phase analogue. Collisionally slowed fragments are al so observed with a much broader angular distribution. The variation in photofragment intensity with adsorbate coverage is consistent with an overlayer that grows by a statistical or stochastic process. Coverage dependent velocity distribution measurements indicate the presence of multiple adsorption phases.