SURFACE PHOTOCHEMISTRY - ADSORPTION AND DISSOCIATION OF CH3CL ON CLEAN AND K-PROMOTED PD(100) SURFACES

The photochemistry of adsorbed CH3 Cl on clean and potassium-dosed Pd(100) surfaces has been studied by illumination with low-intensity UV light from a high-pressure Hg lamp. The effects of illumination were established by post-irradiation thermal desorption, Auger and photoelectron spectroscopic measurements. Evidences are presented for photodissociation of the C-Cl bond to give surface bound methyl group coadsorbed with chlorine. The thermal decomposition of the surface methyl is accompanied by desorption of methane, and small amounts of ethane and ethylene. The presence of preadsorbed potassium greatly enhanced the extent of photodissociation of the C-Cl bond. The efficiency of potassium adatoms depended on its amount, i.e., on the work function of the coadsorbed systems. From the study of the wavelength dependence it is concluded that in the photodissociation of CH3-Cl the optical excitation of the substrate to produce photoelectrons plays a dominant role.