PHOTON AND ELECTRON-STIMULATED DESORPTION OF EXCITED ALKALI-METAL ATOMS AND CN MOLECULES FROM ALKALI-HALIDE SURFACES

Recent advances in photon- and electron-stimulated desorption of excit ed alkali-metal atoms and CN molecules are discussed. The role of defe cts created by photon and electron irradiation leading to surface meta lization is particularly emphasized in the desorption mechanisms. Two mechanisms are proposed for the creation of excited alkali-metal atoms : (1) appropriate to the low-temperature regime, the first mechanism a ssumes that surface exoergic reactions between alkali-metal dimers and halogen atoms produce desorbed excited alkali-metal atoms, the surfac e reactants being formed by radiation-initiated defect processes, and (2) the second mechanism assumes that the gas-phase excitation of grou nd-state alkali-metal atoms by primary electrons produce the excited a lkali-metal atoms. The mechanism responsible for CN desorption may be described in three steps: (1) pre-irradiation produces alkali-metal ri ch surfaces via defect-mediated processes, (2) when the surface is exp osed to CO2 and N-2, surface reactions generate CN molecules bound to the alkali-rich surface, and (3) electron or photon bombardment induce s the desorption of excited CN molecules from the surface by direct bo nd-breaking.