K-shell vacancy production and sharing in (0.2-1.75) MeV/u Fe, Co + Cr collisions

K-shell ionization cross sections measured in the near-symmetric collision systems Fe and Co + Cr at 0.2-1.75 MeV/u energies are reported. The cross section values have been corrected for multiple ionization in the outer (L, M) shells by using the energy and yield shift method. Mean ionization probabilities per electron in the outer shells have been estimated. In the Fano-Lichten model of quasimolecular excitation, 2pσ molecular orbital (MO) ionization cross sections and mean 2pσ-1sσ MO vacancy sharing probabilities were obtained. The present 2pσ MO ionization cross sections could be explained at higher (≥ 1 MeV/u) bombarding energies by an one-step process (Briggs model using SCA calculations with relativistic hydrogenic wave functions and binding correction). The remaining discrepancy between experiment and direct ionization model at lower energies could not be reduced by considering the contribution of single collision two step or multiple collision processes. The vacancy sharing results show that an exponential dependence of the vacancy sharing in function of reciprocal velocity is less fulfilled at higher (≥1.5 MeV/u) energies. Concerning the present multiple ionization data, the Cr M-shell probability is comparable with that of the Cr L-shell for both collision systems, in contrast with the results for the projectile. In the latter case, a larger M-shell multiple ionization in comparison with that of the L-shell is found. The result for the target atom could be qualitatively explained by a rapid partially filling of the M-shell vacancies within the solid target. PACS: 34.50.Fa; 32.30.Rj