Self- and foreign-gas-broadened lineshapes in the ν1 band of NH3

Precise N₂, O₂, H₂, Ar, He, and self-broadenings and shifts have been obtained for Q- and R-branch transitions in the ν₁ fundamental band of ammonia from simultaneous fits of low-noise, high-resolution difference-frequency laser spectra at pressures from 0.07 to 27 kPa (0.5-200 Torr). Observed lineshapes exhibit significant deviations from the conventional Voigt profile, which may be attributed to Dicke narrowing and/or speed-dependent broadening. At the higher pressures, line mixing is evident and must be included in the fits. For self-broadening, line mixing is dominated by collisional tunneling transitions, whereas for the non-polar buffers, rotational relaxation among selected K states is the primary mixing mechanism.