Profile distortion of helium emission lines arising from excitation mechanisms

Abstract

In our experiment, measurements of pressure broadening of the helium emission line () from a gas discharge at liquid nitrogen temperature have been carried out using a scanning Fabry - Perot interferometer. The variation of the line width with number density was found to be nonlinear at low gas pressures which has been qualitatively explained previously, in relation to other spectral lines, in terms of non-thermal Doppler broadening which arises from momentum transfer associated with collisional excitation of short-lived states. In describing the results of these measurements we give a semiquantitative discussion of the excitation mechanisms and their effects on the pressure-broadened line profiles. These are compared with the somewhat different effects observed in the corresponding singlet line - .