Knowledge Bank

Asymmetric line shapes have been observed for infrared transitions of Ar-broadened $HFa$ and were fit to Dicke-narrowed profiles with an empirical partial correlation between velocity- and state-changing collisions. That analysis yielded measured broadening and shifting coefficients in excellent agreement with the thermally-averaged values calculated from exact quantum close-coupled scattering cross-section based on a realistic van der Waals $potentialb$. However, some anomalies in the sense of the asymmetries and the magnitude and J dependence of the velocity-changing rates remained, which subsequently were addressed classically by Joubert $etal.c$ and quantum mechanically by Demeio $etal.d$. Here, we reexamine those line shapes with the correlated speed-dependent strong-collision Dicke-narrowed profiles described above using the reliable energy-dependent cross-sections of Green and Hutson. For HF/Ar below one atmosphere, Dicke narrowing dominates the speed dependence.