Asymmetries and correlations in speed-dependent Dicke-narrowed line shapes of argon-broadened HF

Asymmetric line shapes observed for infrared transitions of Ar-broadened HF [A.S. Pine, J. Chem. Phys. 101, 3444 (1994)] were fit to Dicke-narrowed profiles with an empirical partial correlation between velocity- and phase-changing collisions. That analysis yielded measured broadening and shifting coefficients in excellent agreement with the thermally averaged values calculated by Green and Hutson [J. Chem. Phys. 100, 891 (1994)] from quantum close-coupled scattering cross-sections based on a realistic van der Waals potential. However, some anomalies in the sense of the asymmetries at low J and the magnitude and J dependence of the velocity-changing rates were noted, and are reexamined here by incorporating speed dependence into the collision parameters of the correlated Rautian profile. The speed dependence of the parameters is calculated from the reliable energy-dependent cross-sections of Green and Hutson. For HF/Ar below one atmosphere, we find that deviations from the conventional Voigt profile are dominated by correlated Dicke narrowing rather than speed-dependent effects, but the latter explain the anomalous asymmetries at low J. (C) 1999 Elsevier Science Ltd. All rights reserved.