Observation of a K x-ray band emitted by the transient C--C system formed at keV energies

The yield and high-energy limit (from 1.1 to 1.5 keV) of a $K$ x-ray band emitted by the transient C-C collision system are reported for 19- to 240-keV carbon ions incident on graphite. This $K$ x-ray band is interpreted as characteristic of the C-C system when the nuclear separation approaches the united-atom limit. A small yield of a similar band produced by other light ions in graphite has been observed; this can be accounted for in part by integrating the C-C yield over the appropriate energy distribution of recoil carbon atoms.