Signature of metastable electrons in highly charged ion surface interactions

Abstract

We present autoionization spectra of metastable Ar(8+) and C(4+), N(5+), O(6+) and Ne(8+) scattering off an Al(111) surface with incident energies down to 5 eV. The unprecedented quality of the experimental data permits the observation of a unique, yet undiscovered peak in the structures originating from the metastable projectiles compared to corresponding ground state configurations. Analyzing the peak positions for different projectile species and velocities we demonstrate that the peak must be ascribed to an above-surface transition under participation of the metastable state.