On the speed-dependent hard collision lineshape models: application to C₂H₂ perturbed by Xe

Three infrared absorption lines of the v band of CH diluted by Xe at pressures ranging from 40 to 300 mbar have been recorded at high resolution near 750 cm, using a tunable diode-laser spectrometer. Their lineshapes have been first analyzed by means of models using either the Dicke narrowing effect or the absorber speed-dependent collisional broadening and shifting. None of these models have given satisfactory results over the full pressure range of the perturber. It is shown that a correct treatment must include both line narrowing effects. We have investigated two possibilities of doing so: a convolution between two profiles corresponding to each effect and a noncorrelated and speed-dependent Rautian profile that we have developed here. The latter lineshape model appears to be the most appropriate.