Differences in inner-shell vacancy production for Ar--C collisions in gas versus solid targets

X-ray spectra are presented for Ar-C collisions in gas and solid (graphite) targets, for collision energies of 80 and 90 keV. In gas targets, with either carbon or argon as the target, inner-shell vacancies are produced essentially only in the argon L shell. For Ar⁺ ions incident on graphite, however, there is a high probability of producing vacancies in the K shell of carbon. These observations are plausibly explained within a diabatic molecular-orbitals framework, and lend strong support to such a description.