Spectra of dense helium excited by electron impact

Abstract

This is an account of the visible and near infrared spectrum of dense helium excited by 160keV electrons. It has been suspected that metastable helium atoms are involved in production of strong 02 and N2 spectra when liquid helium doped with these elements is excited by electron impact. This led to an investigation of dense helium gas spectra and the identification in pure gaseous and liquid helium spectra of atomic transitions and the molecular transitions. The absence of other spectral lines suggests that the Hornbeck-Molnar threshold lies between 22.92eV and 23.01eV. The intensity of light emitted from gaseous helium is much greater than from liquid helium, an effect that is not accounted for. Calculations of the excited state populations of helium gas at 4.2°K and 200Torr pressure, bombarded by luA of 160keV electrons, are reported and comments made on the approximations used.