Ionization of the 3dsigma molecular orbital in heavy-ion collisions

As suggested previously, in a heavy-ion collision the sum of the total L-vacancy-production cross section of the higher-Z partner and of the K-vacancy-production cross section of the lower-Z partner, close to K-L level-matching conditions, represents the vacancy-formation cross section in the 3dsigma molecular orbital. It is found empirically that at a given projectile velocity v/sub 1/ the 3dsigma cross section depends mainly on the united-atom Z, independent of the projectile Z (Z/sub 1/), between Z/sub 1/ = 28 and 53. A united-atom ionization model of Briggs is evaluated in the semiclassical approximation. The results provide an upper-limit estimate for the 3dsigma cross section, which reproduces quantitatively its empirical v/sub 1/ and Z dependence and its order of magnitude. The results do not imply, though, that other vacancy-production mechanisms may not be as or more important than ionization.