Pressure-broadened infrared linewidths of HF:Ar and HCl:Ar at moderate densities

The widths of several HCl and HF absorption lines broadened by 10 to 140 atm of argon have been measured using a tunable optical parametric oscillator. The lower pressure data yield values for the linear pressure-broadening coefficients. The data taken at higher densities are used to obtain corrections to the linewidth which are second order in the density. These second density effects are compared with a formal theory for the absorption coefficient at moderate densities due to Albers and Oppenheim, as well as with measurements of the diffusion coefficient obtained in other experiments.