Self-broadening in singlet spectral lines of helium

The emission profiles of five lines in the singlet spectrum of helium, lambdalambda492.2, 501.5, 504.7, 667.8 and 728.1 nm, have been studied under high resolution to test some aspects of line-broadening theory, particularly as it is applied to the resonance interaction. The source was a weak d.c. discharge at 77 or 273 K; the pressure range was 0-10 Torr. Self-absorption was shown to be negligible in separate experiments. Profiles were recorded digitally and analysed by computer into Lorentzian and Gaussian components. The results show that the observed profiles of all the lines are influenced to varying degrees by excitation mechanisms; a discussion of these effects is given. They prevent a quantitative interpretation of lambdalambda492.2 and 667.8 nm, and limit the accuracy of the results for the other lines. Possible experiments to circumvent the difficulties encountered in the present work are discussed. (author)