K-vacancy production in heavy-ion collisions. II. Multiple- and single-collision excitation in the2pσmolecular orbital

The present paper, one of a four-part series, examines $K$-vacancy cross sections in collisions of symmetric and near-symmetric systems produced with 12-60-MeV Br, 200-330-MeV Kr, 15-80-MeV I, 326-470-MeV Xe, and 90-110-MeV Pb beams. Cross sections are discussed from the point of view of molecular-orbital formation during the collision. In that model, the summed $K$-vacancy cross sections of both collision partners represents essentially the total $2p\sigma$ vacancy cross section in the outgoing part of the collision. Experimental summed cross sections using solid targets can have appreciable contributions from multiple-collision effects, which are computed in detail. Proposed single-collision mechanisms of $2p\sigma$ vacancy formation are also examined, but none can be established with certainty. The sharing of $2p\sigma$ vacancies on the outgoing part of the collision between the $K$ shells of two collision partners is found to agree well with a previously derived formula based on the Nikitin-Demkov long-range coupling model.