K-shell ionization probability in energetic nearly symmetric heavy-ion collisions

Impact-parameter-dependent $K$-x-ray emission probabilities for the projectile and target atoms have been measured in 35-MeV Cl on Cl, Cl on Ti, and Cl on Ni collisions. The sum of projectile plus target $K$-shell ionization probability is taken as a measure of the total $2p\sigma$ ionization probability. The $2p\pi -2p\sigma$ rotational coupling model is in clear disagreement with the present results. On the other hand, the sum of probabilities is reproduced both in shape and absolute magnitude by the statistical model for inner-shell ionization. The $K$-shell ionization probability of the higher-$Z$ collision partner is well described by this model including the $2p\sigma -1s\sigma$ vacancy-sharing probability calculated as a function of the impact parameter.