Photodissociation of CH3I on Cu(110)-I:: surface effects on dissociation pathways

The lambda = 337 nm photodissociation of CH3I adsorbed on an iodided Cu(110) surface is found to have an enhanced cross-section compared with that in the gas phase at this wavelength. This enhanced cross-section is found to be maximal for the second adsorbed layer of CH3I and diminishes quickly for layers further removed from the surface. Time-of-flight measurements on the CH3 photofragments find a bimodal translational-energy distribution, which is assigned to neutral photodissociation via CH3 + I(P-2(3/2)) and CH3 + I*(P-2(1/2)) channels. The probability that dissociation proceeds via the higher-energy I* channel is enhanced compared with that in the gas phase at the same wavelength. This behaviour is the reverse of that observed for the same molecule at shorter photolysis wavelengths on other surfaces. (C) 2000 Elsevier Science B.V. All rights reserved.