Energy loss of slow C₆₀⁺ ions during grazing scattering from a KCl(001) surface

The energy spectra of 1–3 keV C₆₀⁺ ions reflected from a KCl(001) surface under grazing incidence are measured with an electrostatic spectrometer. Although both nuclear and electronic energy losses are expected to be almost completely suppressed in the grazing scattering of such extremely low energy ions (v∼0.01 a.u.) from the wide-band-gap insulator surface, we observe anomalously large energy losses ranging from ∼25 eV (θ_i=1°) to ∼100 eV (θ_i=6°). Fragmentation of C₆₀⁺ ions via sequential C₂ loss is also observed during grazing scattering. We find a strong correlation between the energy loss and the fragmentation. From these results the observed anomalous energy losses are attributed to the internal excitations of C₆₀⁺ ions.