L-vacancy production in near-symmetric heavy-ion collisions (Z≳35)

The authors have measured the projectile and target $L$ x-ray spectra and cross sections for 41-MeV Ta projectiles bombarding thin targets between Ag and Th and for 17-60-MeV collisions of Ho on Ho, Au on Au, Pb on Pb, and U on Th. These cross sections, as well as those measured elsewhere, are examined in terms of a simple vacancy-sharing model involving the $4f\sigma$ and $3d\sigma$ molecular orbitals (MO). From the $\frac{L{\beta }_1}{L\alpha }$ x-ray intensity ratios it is found that in symmetric collisions the $4f\sigma$ MO correlates to the $2p_{\frac{3}{2}}$ level of the collision partners (correlation rule of Barat and Lichten). As the asymmetry of the collision system increases, there is an increasing tendency for the $4f\sigma$ MO to correlate to the $2s$ level of the lower-$Z$ collision partner (correlation rule of Eichler and collaborators). The physical basis for the shift of the $4f\sigma$ MO correlation is discussed.