Collisional Broadening Coefficients in the ν4 Band of NH3 Perturbed by He and Ar

Abstract

He- and Ar-broadening coefficients have been measured for 62 absorption lines of NH3 at 296 K in the P branch of the ν4 band, using a high-resolution Fourier transform spectrometer. These lines with J values ranging from 2 to 9 are located in the spectral range 1450–1600 cm−1. The collisional widths are obtained by modeling each absorption line with a Voigt profile. The results are compared with those calculated from a semiclassical model including a second-order Legendre polynomial expansion with adjustable parameters for the intermolecular potential. The experimental and theoretical broadening coefficients have the same behavior with J and K: they roughly decrease as J increases and, except for K = 0, increase with K for a given J value. These variations are small for NH3–He and more significant for NH3–Ar. The calculations give a satisfactory agreement with the data for both perturbers but exaggerate the K dependence of the broadening coefficients, especially for J ≥ 7.