Noble-gas broadening of the Li resonance line

Abstract

The normalized fluorescence spectrum of the Li 6708-Å resonance line perturbed by the noble gases has been measured for 100 Å either side of the resonance line, at a temperature of 400 ± 10°C. The noble-gas pressure range of 100-1800 Torr was investigated. It was observed that the line wings scale linearly with this pressure for $2<\left|\Delta \lambda \right|<\mathrm{}100\mathrm{}$ Å, and it was was demonstrated that a Lorentzianbroadened line core can be observed for this pressure range. The Li density was ∼ ${10}^{10}$/${\mathrm{cm}}^3$ and was varied to establish the fluorescence spectrum in the limit of no radiation entrapment. The central region of the line has been measured with high resolution and compared to calculated profiles due to the various fine structure and isotopic line components, each broadened by a convolution of Lorentz, Doppler, and instrumental profiles. The shift and Lorentz broadening rates, as well as the wavelengths for transition to non-Lorentzian behavior, are reported. In contrast to the heavier alkali-metal-noble-gas cases, no distinctive far-wing features such as satellites or sharp inflections are observed. This is consistent with the much larger collision velocities for the Li case.