Ejected-Atom Energy Spectra from Electronically Excited Rare-Gas Solids

The energy spectra of atoms ejected as a result of the electronic excitation of rare-gas solids by keV electrons and ${\mathrm{He}}^{+}$ ions are presented. These spectra are found to have a well-defined structure with two distinct features indicative of nonradiative electronic relaxation processes. The higher-energy peak is due to radiative decay of vibrationally relaxed dimers that are either desorbed or weakly bound to the surface. The lower-energy peak exhibits a trend from Ar to Xe which is shown to be determined by subsurface dimer decays and is consistent with the trend in the cohesive energy.