High pressure line shapes for Cs D1 and D2 lines and empirically informed interaction potentials

Line shapes for the Cs D1 (6 2S1/2-6 2P1/2) and D2 (6 2S1/2-6 2P3/2) transitions for He, Ne, and Ar collisions at pressures of 100-2280 Torr and temperatures of 294-448 K have been experimentally observed and compared to predictions from the Anderson-Talman theory. Asymmetry in the core of the line shape is generally correlated with shift rates, except for the Ne D1 line, which is red shifted, but blue shaded. There is a dramatic difference between the D1 and D2 lines for the shift and asymmetry parameters, particularly for He and Ne. A blue satellite is observed in the far wing of the D2 line at 827.2, 833.4, and 834.9 nm for He, Ne, and Ar, respectively. The amplitude of the blue satellite scales linearly with pressure, exceeding 0.014% of the peak cross-section at 2280 Torr. Modest red shoulders are observed for both the D1 and D2 lines associated with extrema in the difference potentials. Existing ab initio potential surfaces require empirical modification to adequately describe the observed spectra. However, the long-range dipole and quadrupole polarizabilities are sufficient to establish the observed broadening and shifting rates. Two distinct sets of difference potentials are developed that adequately represent the line shape observations. Predictions for the temperature dependence of the collision induced shift are significantly different for the two sets of empirically modified potentials.