Ar-broadening coefficients in the ν₇ band of ethylene at low temperatures

Using a tunable diode-laser spectrometer adapted with a low temperature cell, the ethylene line-broadening by argon is measured for some vibrotational lines in the ν band at different temperatures varying from 198.2 to 273.2 K. The collisional half-widths obtained by modeling each spectral line with the simple profile of Voigt are always smaller than those derived from the Rautian model which takes into account the Dicke effect. From these collisional half-widths, for each line, the broadening coefficients are obtained for different temperatures. Calculations of the corresponding broadening coefficients are made independently on the basis of the Robert-Bonamy formalism with exact trajectories using an atom-atom intermolecular potential model. The temperature dependence parameters n are determined experimentally and theoretically by comparing the experimental and theoretical broadening coefficients of the same lines at room and different low temperatures.