Semiempirical model for angular distribution of electrons emitted in metastable atom-atom collisions

Electron angular distributions from ionization in collisions of $\mathrm{He}\left(2\mathrm{}{}_{}{}^{1,3}{}_{}{}^{}S\right)$ and $\mathrm{Ar}\left({}_{}{}^1{}_{}{}^{}S\right)$ have been studied in terms of molecular-orbital correlation diagrams and a semiclassical and probabilistic model for the collision process. Consideration of the united-atom limit for this system indicates that the electronic angular momenta $\lambda =0, 1, \mathrm{and} 2$ play an important role. The interaction potential responsible for electron emission was assumed to decrease exponentially with increasing distance, and was parametrized by fitting experimental results at a fixed collision energy. The values of the parameters show that $\lambda =0\mathrm{}$ is the dominant partial wave and lead to backward-peaked distributions. Calculations performed at other energies show an increasing anisotropy with increasing collision energies.