Deexcitation of Fast He, Ne, and Ar Metastable Atoms in Various Gases

Abstract

Absolute cross sections for the deexcitation of $\mathrm{He}\left(2\mathrm{}{}_{}{}^1{}_{}{}^{}S\right)$ and of $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$ metastables by ${\mathrm{N}}_2$ and Ar have been measured over the energy interval from 150 to 1600 eV using an optical technique. The $2{}_{}{}^1{}_{}{}^{}S$ cross sections are found to be as much as 50% larger than the $2{}_{}{}^3{}_{}{}^{}S$ cross sections for deexcitation by ${\mathrm{N}}_2$, while for Ar the two cross sections are nearly equal at these energies. The cross sections all lie in the range of 7-20 ${\mathrm{\AA }}^2$ and decrease with increasing energy. Deexcitation cross sections have also been measured by collecting slow ions for mixed beams of He metastables in ${\mathrm{N}}_2$, Ar, and ${\mathrm{C}}_2$ ${\mathrm{H}}_2$ and for mixed beams of Ar metastables in ${\mathrm{C}}_2$ ${\mathrm{H}}_2$ and Ne metastables in Ar. These measurements are in the energy range from 50 to 600 eV. They do not discriminate between different metastable states, but the results exhibit an energy behavior similar to that of the state-separated measurements and are consistent with those measurements when comparison can be made.