Dicke narrowing and pressure broadening in the infrared fundamental band of HCl perturbed by Ar

Dicke narrowing due to state preserving but velocity changing collision has been observed in several high-J vibration-rotation transitions of the fundamental band of HCl with Ar as the collision partner. Because of the long wavelength of radiation and the small diffusion coefficient, the narrowing occurs at a relatively low pressure of ∼200 Torr. A difference frequency laser system was employed for the studies of linewidths and lineshapes over the temperature range of 297–420 K. The results were analyzed using the diffusion model.