Line Broadening and Mixing in NH₃ Inversion Doublets Perturbed by NH₃, He, Ar, and H₂

ISSN： 0022-2852

Source： Journal of Molecular Spectroscopy, Vol.210, Iss.2, 2001-12, pp. : 275-283

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Abstract

Measurement of absorption by pure ammonia and NH₃–(H₂, He, and Ar) mixtures in the P branch of the ν₄ band at room temperature have been made with a high-resolution Fourier transform spectrometer. Least squares fits of the spectra using different techniques are used for the analysis of the evolution with pressure of the absorption shape for a number of ^PP inversion doublets. Intensities, half-widths, and line-coupling parameters are determined, demonstrating the great importance of line-mixing effects. The results are compared with values calculated using a semiclassical model. The latter explains most of the features of the line-broadening and the J and K dependencies of line-coupling for pure NH₃, whereas poorer results are obtained for line-mixing in mixtures. The most striking and original result is the very large amount of coupling between the symmetric and antisymmetric components, which can reach up to 80% of the width in the case of pure NH₃. Also remarkable is the very strong influence of the rotational quantum number K. © 2001 Elsevier Science