Argon-broadening coefficients in the ν5 band of acetylene at room and low temperatures

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Ar-broadening coefficients have been measured in the P- and R-branches of the ν 5 fundamental band of C 2H 2 for 30 lines at room temperature and 8 lines at −100 °C, using a tunable diode-laser spectrometer. These lines with J values ranging from 2 to 27 are located in the spectral range 665–795 cm −1. The collisional widths are obtained by fitting each absorption line with three lineshape models: the Voigt profile, the Rautian profile accounting for the Dicke narrowing effect, and a general Rautian profile including the absorber speed-dependent collisional broadening. The latter model provides significantly larger broadening coefficients than the Voigt model. These coefficients are also calculated from a semiclassical theory performed by using a simple intermolecular potential with two adjustable parameters. Finally, the temperature dependence of the broadening coefficients has been determined both experimentally and theoretically.