Model quantum-mechanical calculations for the Penning ionization of Ar by He(2³S)

Using model potential curves V*, Gamma and V + , quantum-mechanical calculations are carried out for the scattering of He(2 3 S) and Ar in the energy range 20-180 meV. Certain simplifying approximations in the theory are made which are discussed in detail. The potential curves are obtained by fitting calculated results to available experimental data. The model potentials derived in this manner reproduce differential and total elastic cross sections. Penning electron energy distributions, and Penning and associative ionization cross sections. The mechanism of quasi-associative ionization can account for as much as 8% of the measured HeAr + ions under typical experimental conditions. It is found that most features of the scattering are adequately explained by a classical theory. Recent experimental results, however, indicate that there may be structure in the energy dependence of the associative ionization cross section. A simple quantum-mechanical explanation is suggested.