Surface and bulk photochemistry of solids

This article reviews aspects of photochemistry on solid surfaces. In order to understand the photo-induced processes a brief introduction is given to the interaction between light and the solid-gas interfaces. The adsorption of molecules on solid surfaces, and the negative ion resonances (NIR) by inelastic electron scattering are briefly discussed; There are three photoinduced processes which occur on surfaces: photoinduced desorption (PID), photoinduced dissociation and photoinduced reactions. The mechanisms of the photoinduced processes are discussed and related to the experimentally determined cross sections. Photoinduced processes are driven: (i) by direct electronic excitation of the adsorbate, (ii) by substrate excitation, (iii) by both adsorbate and substrate excitation, or (iv) by charge transfer dissociation. The usual experimental methods and the light sources are presented. Most of the experimental examples deal with photo-stimulated experiments in the IR-visible and UV region. In some examples photon stimulated desorption of ions of physisorbed molecules is studied by using VUV synchrotron radiation in the energy range between 13-40 eV. In addition to desorption and dissociation, photo-excited molecules can react with each other and form new chemical bonds leading to new species on the surface. Photoinduced polymerizations of formaldehyde on Ag(ll I) occur after irradiation with light at lambda = 355 nm.