Threshold of ion-induced kinetic electron emission from a clean metal surface

Electron emission from clean gold under impact of ${\mathrm{H}}^{+}$ or singly charged rare-gas ions in their ground state has been investigated at the kinetic emission threshold, measuring both the emission statistics and total yields by means of counting techniques. As we are able to subtract any contribution from potential emission, we observe kinetic emission well below the threshold for sufficient energy transfer from projectiles onto quasifree metal electrons and relate this contribution to quasimolecular autoionization in close collisions between the neutralized projectiles and metal ion cores.