Experimental and theoretical study of line mixing in NH_3 spectra.II.Effect of the perturber in infrared parallel bands

摘要

In a previous paper [J.Chem.Phys.116,7544 (2002) (Paper I)]a model,base 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_3 with H_2 and Ar.Measurements have been made at room temperature in the regions of the upsilon_2 and upsilon_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_3-X potentials 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_3-Ar and NH_3-H_2 are qualitatively similar to those observed for NH_3-He but quantitative differences exist,particaularly 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 upsilon_2 bands of NH_3 diluted in H_2,opening promising perspectives for the remote sensing study of planetary atmospheres.