THE ADSORBATE STATE SPECIFIC PHOTOCHEMISTRY OF DIOXYGEN ON PD(111)

The ultraviolet-photochemistry of molecularly adsorbed oxygen on Pd (111) has been studied using pulsed laser light with 6.4 eV photon energy. Three processes occur upon irradiation: desorption of molecular oxygen, conversion between adsorption states, and dissociation to form adsorbed atomic oxygen. By using time-of-flight spectroscopy to detect the desorbing molecular oxygen and post-irradiation thermal desorption spectroscopy (TDS) to characterize the adsorbate state, a detailed picture of the photochemical processes is obtained. The data indicate that the O2 molecules desorbing with low translational energies from the saturated surface as well as the conversion of adsorbed molecules between binding states are induced by the photoinduced build-up of atomic oxygen on the surface. Analysis of a proposed reaction model reproduces the observed data and yields detailed rates. Polarization analysis indicates that the photochemical processes are initiated by electronic excitations of the substrate. © 1990 American Institute of Physics.