NEUTRALIZATION OF HE+ AND HE-2+ ON PB SURFACES

The neutralization of slow He+ and He2+ ions on Pb surfaces allows the study of Auger capture, resonant capture into autoionizing states and of a Landau-Zener-type two-state charge exchange process. In the primary energy range of 300 eV to 6 keV the processes are experimentally accessible by measuring the reflected ion energy spectra and the secondary electron energy spectra. The results lead to estimates of the transition rates (1.7-3.0 x 10(15) s-1 for Auger capture and 4.2 x 10(15) s-1 for resonant capture into autoionizing states) of the charge exchange processes and of the distances (3.55-4.0 angstrom for the Landau-Zener process) where these processes in front of the metal surface occur.