Exchange Excitation in Helium: Excitation Functions for the4S3,3P3, and3D3Levels

Abstract

Excitation functions and the pressure dependences of the apparent cross sections for the $4{}_{}{}^3{}_{}{}^{}S$, $3{}_{}{}^3{}_{}{}^{}P$, and $3{}_{}{}^3{}_{}{}^{}D$ levels are obtained for energies between 50-500, 50-600, and 50-500 eV, respectively, and for pressures in the region 1.0-10 μ Hg. The excitation function of the $4{}_{}{}^3{}_{}{}^{}S$ is found to be purely monotonically decreasing with energy at a slope of a - 3.0 ± 0.2. The $3{}_{}{}^3{}_{}{}^{}D$ and to a lesser extent the $3{}_{}{}^3{}_{}{}^{}P$ excitation functions are composed of two energy dependences, a slow one attributed to mixed $F$-level cascade, and an initially dominant fast component due to exchange excitation. The fast component falls as ${\mathrm{}\left(\mathrm{energy}\right)\mathrm{}}^{-3.5\pm 0.2}$ and ${\mathrm{}\left(\mathrm{energy}\right)\mathrm{}}^{-3.7\pm 0.5}$ for the $3{}_{}{}^3{}_{}{}^{}P$ and $3{}_{}{}^3{}_{}{}^{}D$ levels, respectively.