Temperature dependence of self-broadening at low densities in singlet spectral lines of helium

Spectra profiles of the helium lines lambda =501.5, 667.8 and 728.1 nm have been studied in emission under high resolution by means of a scanning Fabry-Perot interferometer for a wide range of discharge temperatures and pressures. The collisional-broadening constants determined from the Lorentzian component of the spectral profiles vary significantly with temperature, especially for the case of lambda =501.5 nm. These departures from the behaviour of pure-resonance broadening suggest that the profiles are distorted as a result of excitation mechanisms and, for the lambda =501.5 nm line, indicate the presence of higher-order terms in the interaction potential.