Self-broadening at low densities in the spectrum of neon

Self-broadening of the transitions at 585.2, 659.9 and 667.8 nm in neutral neon has been studied in emission by means of a scanning Fabry-Perot interferometer. These lines all connect to the strong resonance level (2p 5 3s 1 P 1 ), and the broadening is dominated by the resonance interaction. The source was a weak discharge run at pressures up to 10 Torr and cooled with liquid nitrogen (77K) or melting ice (273K). Data were recorded and analysed digitally; most spectral profiles were found to be well represented by the Voigt function, though evidence of slight profile distortion, attributed to excitation mechanisms, was found for all three lines under certain conditions of temperature and pressure. The Lorentzian widths varied linearly with pressure. All experiments were carried out with the natural mixture of isotopes and a sample enriched in 20 Ne and no significant differences in the broadening were observed. When allowance was made for profile distortion the collisional broadening was found to be independent of the spectral line and of the temperature to within experimental error, in accordance with the prediction of theory for the case of pure resonance broadening. The measured broadening constants were 6.13(16) at 77K and 6.19(28) at 273K, to be compared with the theoretical value of 6.28(25), in all units of 10 -20 cm -1 cm 3 per atom. The Lorentzian width of lambda 585.2 nm extrapolated to zero pressure at 77K was found to exceed the radiation width of the line, in agreement with earlier workers, but only by 0.7(5) mK which is small enough to be attributed to excitation mechanisms. lambda 585.2 nm shows a small shift to longer wavelength with increasing pressure at both temperatures; this is attributed to higher order terms in the interaction potential.