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

Three infrared absorption lines of the nu(5) band of C2H2 diluted by Xe at pressures ranging from 40 to 300 mbar have been recorded at high resolution near 750 cm(-1), 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. (C) 1997 Academic Press.