MEASUREMENT OF YIELDS FOR ELECTRON-EMISSION FROM SURFACES UPON IMPACT OF LASER-EXCITED AR-ASTERISK(4P) AND KR-ASTERISK(5P) ATOMS

A laser method for the determination of the electron emission coefficient-gamma for the impact of low laser-excited rare gas atoms Rg*[mp5(m + 1)p 3D3] on surfaces is described. It is based on controlled partial depletion of metastable Rg *[Mp5(m + 1)s P-3(2)] atoms in a collimated beam by two-step laser photoionization in combination with saturated laser excitation of the metastable (P-3(2)) atoms to the (3D3) level at the surface. The method simultaneously yields the coefficients-gamma for the metastable Rg*(P-3(2)) and the laser-excited Rg*(3D3) atoms. As an application, we report gamma-values corresponding to the impact of Ar*(P-3(2), 3D3) and Kr*(P-3(2), 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 gamma-values for the four excited rare gas species shows a complex excitation energy dependence.