K-shell vacancy production in collisions of aluminum, silicon, chlorine, and argon ions with solid and gas targets

$K$-shell vacancy-sharing ratios have been measured for beams of aluminum, silicon, chlorine, and argon with energies between 0.7 and 16 MeV incident on solid targets of aluminum and copper, and gas targets of sulphur and argon. Values of these sharing ratios as a function of the reciprocal of the velocity of the incident ions have been observed to deviate from predicted exponential behavior under experimental conditions such that the deviations cannot be ascribed to multiple-collision effects. Results are presented for measurements of $\sigma \left(2p\sigma \right)$, the cross section for production of vacancies in the $2p\sigma$ molecular orbital, and of $\sigma \left(1s\sigma \right)$, the cross section for direct production of vacancies in the $1s\sigma$ molecular orbital, for aluminum ions with kinetic energies between 0.7 and 2.5 MeV incident on argon atoms. Comparisons are made between these measured cross sections and appropriate calculations.