Self-Broadening and the Resonance Oscillator Strengths in Krypton

Abstract

By means of a direct-recording Fabry-Perot interferometer, the emission profiles of five red lines in krypton were obtained under widely varying conditions of gas density and temperature. The profiles were analyzed in various ways, and the Lorentz components determined as functions of density. In two of the lines studied, 7587 and 7685 Å, the observed broadening coefficients could be attributed almost entirely to resonance interaction in the lower levels. From the measured broadening coefficients, the oscillator strengths of the resonance lines were calculated as ${}_{}{}^1{}_{}{}^{}f\left(1164\mathrm{} \AA \right)=0.184\mathrm{}$ and ${}_{}{}^3{}_{}{}^{}f\left(1236\mathrm{} \AA \right)=0.204\mathrm{}$ with estimated error limits of 10% (arising mostly from uncertainties in the broadening constant). These values are more than 30% larger than recent theoretical calculations. Linear extrapolation of the Lorentz width to zero gas density provides some evidence of the anomaly found in helium and neon, which has been attributed to an additional "coupling width" at very low density. The study of the strongly resonance-broadened line 7587 Å was extended up to pressures of 20 mm Hg at 90°K. It was found that the rate of self-broadening decreased at high pressure, where the line was symmetrical but not of the Voigt shape; also, the maximum was shifted towards higher frequencies. Possibilities of relating these effects to theoretical considerations are discussed. In the lines whose lower levels are metastable, the ratios and temperature coefficients of width and shift are consistent with broadening due to van der Waals forces obeying an $r^{-6\mathrm{}}$ potential law.