Experimental and theoretical study of line mixing in NH[sub 3] spectra. II. Effect of the perturber in infrared parallel bands.

In a previous paper [J. Chem. Phys. 116, 7544 (2002) (Paper I)] a model, based on the energy corrected sudden approximation, was proposed for the construction of the line-mixing relaxation matrix. It was successfully tested by comparisons with measured infrared spectra of ammonia–helium mixtures. The present paper extends this preliminary study by considering mixtures of NH[sub 3] with H[sub 2] and Ar. Measurements have been made at room temperature in the regions of the ν[sub 2] and ν[sub 1] bands for pressures up to several hundred atmospheres. As in Paper I, the relaxation operator is constructed, within the impact approximation, using the ECS approximation. The data required are dynamical factors (which can be predicted from the NH[sub 3]–X potential energy surface) and a scaling length (adjusted using line broadening data). Comparisons between measured and calculated absorptions demonstrate the quality of the model which satisfactory corrects for the large deviations with respect to the purely Lorentzian behavior. Line-mixing effects for NH[sub 3]–Ar and NH[sub 3]–H[sub 2] are qualitatively similar to those observed for NH[sub 3]–He but quantitative differences exist, particularly when intra- and interbranch couplings are considered. Finally, the proposed model leads to very satisfactory results in the wings of both the purely rotational and ν[sub 2] bands of NH[sub 3] diluted in H[sub 2], opening promising perspectives for the remote sensing study of planetary atmospheres. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]