End-Point Energy Variations in the Noncharacteristic Radiation Produced by S, C1, Ar, K, Ca, and Ti Bombardment of Si

The noncharacteristic radiation observed in heavy-ion bombardment of Si was investigated with 200-keV ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$, ${}_{}{}^{35,37}{}_{}{}^{}\mathrm{Cl}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$, ${}_{}{}^{39,41}{}_{}{}^{}\mathrm{K}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, and ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ti}$ projectiles ($16<~Z<~22$) on Si. The high-energy tail of the noncharacteristic radiation is observed to shift to higher energies as projectile $Z$ is increased. The observed end-point energy shifts are in agreement with the interpretation that the radiation arises from the radiative decay of a projectile $2p$ vacancy in the quasimolecule formed by the projectile and the target atom during the collision.