Velocity dependence of the cross sections for Penning and associative ionization of H and D atoms byHe(2S3)metastable atoms

Abstract

The velocity dependence of both the Penning and associative ionization cross sections ${\sigma }_{\mathrm{PI}}$ and ${\sigma }_{\mathrm{AI}}$ for the $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)+\mathrm{H}$ interacting system as well as total ionization cross section ${\sigma }_{\mathrm{TI}}$ is measured for the relative velocity range 1900-5300 m/sec (0.015-0.10 eV energy range) in a crossed-beam experiment by a time-of-flight technique. Characteristic cross-section ratios $\frac{{\sigma }_{\mathrm{AI}}}{{\sigma }_{\mathrm{TI}}}$ and the relative magnitudes of the cross sections ${\sigma }_{\mathrm{AI}}$, ${\sigma }_{\mathrm{PI}}$, and ${\sigma }_{\mathrm{TI}}$ are reported. The experimental results concerning the total ionization cross section are in very good agreement with previous theoretical work, but the experimental values of the ratio $\frac{{\sigma }_{\mathrm{AI}}}{{\sigma }_{\mathrm{TI}}}$ are found to be higher than theoretical values, especially at low energies. A numerical solution of the Schrödinger equation with a complex potential is performed to interpret both the results on the $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)+\mathrm{H}$ system and our previously published results on the $\mathrm{He}\left(2\mathrm{}{}_{}{}^1{}_{}{}^{}S\right)+\mathrm{H}$ system. A truncated width is used for the calculation of the associative cross sections. It is observed that an exponentially shaped autoionization width $\Gamma \mathrm{}\left(R\right)={\mathrm{Ae}}^{-\frac{R}{B}}$ is satisfactory and that the width for the $\mathrm{He}\left(2\mathrm{}{}_{}{}^1{}_{}{}^{}S\right)+\mathrm{H}$ system is nearly equal to the width for the $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)+\mathrm{H}$ system.