New interpretation of Penning spectra from alkali-metal atoms chemisorbed on metal surfaces

Penning deexcitation spectra of alkali atoms adsorbed on metals show an intense peak at the Fermi level for coverages around the work-function minimum. This strong electron emission is assigned to the decay of a core-excited negative ${\mathrm{He}}^{\mathrm{-}}$ ion created by resonance transition of a substrate electron into the affinity level of the metastable rare-gas atom. The formation of this species also easily provides an explanation for the observed ${\mathrm{He}}^{\mathrm{*}}$ singlet-triplet conversion.