SIGNATURE OF METASTABLE ELECTRONS IN HIGHLY-CHARGED ION-SURFACE INTERACTIONS

We present autoionization spectra of metastable Ar-8 divided by and C- 4 divided by, N5+, O6+, and Ne8+ scattering off an Al(111) surface wit h incident energies down to 5 eV. The unprecedented statistical qualit y of the experimental data permits the observation of structures origi nating from the metastable projectiles compared to corresponding groun d-state configurations. Analyzing the peak positions for different pro jectile species and velocities we demonstrate that the peak must be as cribed to an above-surface transition with the participation of the me tastable state.