Measurement of yields for electron emission from surfaces upon impact of laser-excited Ar*(4p) and Kr*(5p) atoms

A laser method for the determination of the electron emission coeflicient γ for the impact of slow laser-excited rare gas atoms Rg*[mp5(m+1)p3D3] on surfaces is described. It is based on controlled partial depletion of metastable Rg*[mp5(m+1)s3P2] atoms in a collimated beam by two-step laser photoionization in combination with saturated laser excitation of the metastable (3P2) atoms to the (3D3) level at the surface. The method simultaneously yields the coefficents γ for the metastable Rg*(3P2) and the laser-excited Rg*(3D3) atoms. As an application, we report γ values corresponding to the impact of Ar*(3P2, 3D3) and Kr*(3P2, 3D3) atoms on several gas-covered metal surfaces. The data show that the electron emission process involves Auger de-excitation and can be interpreted as Penning ionization of adsorbed molecules. Comparison of the γ values for the four excited rare gas species shows a complex excitation energy dependence.