Recombination ofHe+andHe++in the Afterglow of a Helium Discharge

Studies of the time dependence of atomic and molecular light intensities, electron density, atomic metastable densities, and electron temperature have allowed the determination of the ${\mathrm{He}}^{+}$-electron and ${\mathrm{He}}^{++}$-electron recombination coefficients as functions of electron density and temperature. The results are in reasonable agreement with the theory of collisional-radiative recombination. The mechanisms controlling metastable densities and heating of the electron gas are discussed. In particular, the disappearance of the $2{}_{}{}^3{}_{}{}^{}S$ metastable atom seems best explained in terms of collisional de-excitation by electrons.