Optical Excitation and Polarization in Low-Energy Collisions ofHe++H2

Abstract

Optical studies of spectral lines produced in collisions of ${\mathrm{He}}^{+}$ + ${\mathrm{H}}_2$ have been made at energies below 700 eV. Lines of atomic hydrogen and helium are the only features observed. Emission cross sections have been measured for Lyman-$\beta$, Balmer-$\alpha$, Balmer-$\beta$, and for the following He i lines: $5876 \AA (3\mathrm{}{}_{}{}^3{}_{}{}^{}D\to 2{}_{}{}^3{}_{}{}^{}P)$, $6678 \AA (3\mathrm{}{}_{}{}^1{}_{}{}^{}D\to 2{}_{}{}^1{}_{}{}^{}P)$, $4471 \AA (4\mathrm{}{}_{}{}^3{}_{}{}^{}D\to 2{}_{}{}^3{}_{}{}^{}P)$. Emission cross sections are also listed at certain selected energies for all spectral lines which have been observed. Polarization measurements have been performed on the Balmer-$\alpha$, the Balmer-$\beta$ and the visible helium lines. Only the Balmer-$\alpha$ line exhibits significant polarization, and the results have been interpreted as indicating that the excited hydrogen atoms dissociate primarily in a direction perpendicular to the ion beam.