Absolute K-shell ionization cross sections have been measured for thin targets of Al, Ti, and Cu for protons in the energy range 0.3–2.0 MeV and for thin targets of Ti, V, Cr, Fe, Ni, Cu, and Ag for oxygen ions in the energy range 1.36–6.4 Mev. The experimental results are compared to the perturbed-stationary-state (PSS) approximation with energy-loss (E), Coulomb (C), and relativistic (R) corrections, i.e., the ECPSSR approximation (Brandt and Lapicki), to the semiclassical approximation (Laegsgaard, Andersen, and Lund), and to a theory for direct Coulomb ionization of the 1sσ molecular orbital [Montenegro and Sigaud (MS)]. The proton results agree within 3% with empirical reference cross sections. Also, the ECPSSR provides best overall agreement for protons. For oxygen ions, ECPSSR and MS predict experimental results satisfactorily for scaled velocities ξ≥0.4. For lower scaled velocities, the experimental cross sections become considerably higher than theoretical predictions for Coulomb ionization. This deviation increases with increasing $Z_1$/$Z_2$; it cannot be explained by electron transfer to the projectile or by ionization due to target recoil atoms.

• Received 19 February 1986

DOI:https://doi.org/10.1103/PhysRevA.34.866