Knowledge Bank

$N2$ and air broadened lineshapes of HF and HCl transitions in the $v=1\leftarrow 0$ bands have been measured at T-295 and 202 K with a high-resolution difference-frequency laser spectrometer. Pressure broadening and shifts and collisional narrowing parameters have been extracted by least squares fitting of several collisional profiles to the spectra. At low pressures, the collisional, or Dicke, narrowing effect causes deviations from the Voigt profile having a Doppler-fixed Gaussian component and yields a measure of the diffusion constants for the hydrogen halides in the buffer gases. At high J, where the pressure shifts are comparable to or larger than the broadenings, a slight asymmetry is observed in the lineshapes which is attributed to statistical correlation between velocity- and states-changing collisions. The ration of air-to-$N2$ broadening varies systematically with rotational level and is always somewhat larger than that given by the relative quadrupolar contributions of $O2$ and $N2$. The temperature variations in the broadening coefficients are also J dependent, deviating significantly from $T-1/2$ and exhibiting opposite behavior for HF and HCl.