Experimental and theoretical study of line mixing in NH3 spectra. II. Effect of the perturber in infrared parallel bands

Abstract

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 NH3 with H2 and Ar. Measurements have been made at room temperature in the regions of the nu2 and nu1 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 NH3-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 NH3-Ar and NH3-H2 are qualitatively similar to those observed for NH3-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 nu2 bands of NH3 diluted in H2, opening promising perspectives for the remote sensing study of planetary atmospheres.

Shifting and line mixing parameters in the ν4 band of NH3 perturbed by CO2 and He: Experimental results and theoretical calculations

“…In other studies, it was shown that line mixing could greatly influence the values of the molecular parameters obtained during fitting processes with assumed line shapes. In fact, line mixing was also taken into accounted in several studies for the m 1 , m 2 , and m 4 bands of NH 3 perturbed by He, Ar and H 2 [5][6][7].…”

Line shift and mixing in the ν4 and 2ν2 band of NH3 perturbed by H2 and Ar

“…Recently, Hadded et al [13] have studied line mixing of 15 inversion doublets of NH 3 perturbed by He, Ar, and H 2 . More recently, these authors [14,15] have measured line mixing effects in the m 1 and m 2 bands of NH 3 at high pressure. They have demonstrated the necessity of take into account line mixing for the treatment of inversion-rotation spectra of NH 3 .…”

Line-mixing between rotational Stark components of CH3F self-perturbed and perturbed by helium: Experimental results and IOS analysis

“…An alternative approach to take LM into account is to build the associated relaxation matrix using the Infinite Order Sudden (IOS) approximation [1,8] or its improved Energy Corrected Sudden (ECS) extension [1,9,10]. IOS/ECS models have enabled precise modeling of LM effects for many systems and types of spectra [1], including hyperfine components due to nuclear spin [11,12] and symmetric-top spectra [13,14]. However, quite surprisingly, as shown in Ref.…”