Spectral dependencies of the quantum yield of photochemical processes on the surface of wide-band-gap metal oxides.: 2.: Gas/solid system involving scandia (Sc2O3) particles

in this article we examine the spectral dependencies of the quantum yields of photoadsorption of such donor molecules as hydrogen, methane, and carbon monoxide on the surface of Sc2O3 particulates when excited in the spectral absorption region of photogenerated hole color centers. Photobleaching of these color centers with light of different wavelengths shows the complexity of their absorption spectrum consisting of overlapping single bands. The spectral dependencies of quantum yields of photoadsorption of the donor molecules and photodesorption of preadsorbed oxygen is described by (a) a kinetic approach and (b) on the basis of the solved continuity equation (charge-conservation law) upon assuming the existence of several types of hole color centers with corresponding single-absorption bands and different photoionization probabilities (different quantum yields of internal photoeffects). The quantum yields of photoadsorption depend on the efficiency of the photophysical processes implicated in carrier photogeneration and carrier transport toward the particle surface together with the probabilities of different secondary chemical reactions on the surface of the solid particulates.