SURFACE AND BULK PHOTOCHEMISTRY OF SOLIDS

This article reviews aspects of photochemistry on solid surfaces. In o rder 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 re sonances (NIR) by inelastic electron scattering are briefly discussed; There are three photoinduced processes which occur on surfaces: photo induced desorption (PID), photoinduced dissociation and photoinduced r eactions. The mechanisms of the photoinduced processes are discussed a nd related to the experimentally determined cross sections. Photoinduc ed processes are driven: (i) by direct electronic excitation of the ad sorbate, (ii) by substrate excitation, (iii) by both adsorbate and sub strate 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 r adiation in the energy range between 13-40 eV. In addition to desorpti on and dissociation, photo-excited molecules can react with each other and form new chemical bonds leading to new species on the surface. Ph otoinduced polymerizations of formaldehyde on Ag(ll I) occur after irr adiation with light at lambda = 355 nm.