Quenching and excitation transfer in then=3helium sublevels in a low-pressure glow discharge

Abstract

The collisional and radiative processes leading in a glow discharge to quenching and and excitation transfer in the $n=3\mathrm{}$ helium sublevels are investigated by means of a laser perturbation method. Laser-induced population perturbations are solutions of coupled rate equations, the coefficients of which are related to radiative coefficients and collisional excitation cross sections. An accurate numerical method of data analysis (the "identification method") is developed in which the rate coefficients are determined so as to minimize the difference between experimental curves and those calculated from the model. In the pressure and current intensity investigated, $P<\mathrm{}10\mathrm{}$ Torr, $i<\mathrm{}50\mathrm{}$ mA, only radiative and atom-atom collision processes contribute to quenching and excitation transfer in the $n=3\mathrm{}$ levels. Numerical identification of the $n=3\mathrm{}$ experiments provides a nearly complete set of rate coefficients and thermally averaged cross sections. In particular, $3{}_{}{}^1{}_{}{}^{}P\rightleftarrows 3{}_{}{}^1{}_{}{}^{}D$ excitation transfers predominate over the $3{}_{}{}^3{}_{}{}^{}P\rightleftarrows 3{}_{}{}^3{}_{}{}^{}D$ ones. This results from the near-resonant character of the He-He* inelastic collision processes.