Abstract
Inner-shell excitation of heavy ions passing through gaseous or solid-state targets is discussed in view of the influence of collisional quenching. An apparently dominating process for collisional quenching is thought to be the capture of target electrons into projectile vacancies. This process successfully explains the oscillatory behaviour which is found for the K-shell photon yield of swift chlorine ions passing through solid foils as a function of the target atomic number.