Narrowing and broadening parameters for H2O lines perturbed by helium, argon and xenon in the 1170–1440 cm−1spectral range

Full quantum calculations of the line shape for H2O perturbed by Ar at temperatures from 20 to 300 K

This work theoretically studied the spectral line shape of H2O perturbed by Ar in the temperature range of 20-300 K for the pure rotational lines below 360 cm-1, as well as three lines (31, 2 ← 44, 1, 54, 2 ← 41, 3, and 73, 5 ← 60, 6) in the v2 band. In order to perform precise dynamical calculations at low collision energies, a full-dimensional long-range potential energy surface was constructed for the H2O-Ar system for the first time to correct the long range of our newly developed intermolecular potential energy surface. Subsequently, the six line-shape parameters (pressure-broadening and -shifting parameters, their speed dependencies, and the complex Dicke parameters) were determined from the generalized spectroscopic cross section by the full quantum time-independent close-coupling approach on this new potential energy surface. Our theoretical results are in good agreement with the available experimental observations. Furthermore, the influence of the speed-dependence and Dicke narrowing effects on the line contour was revealed by comparing the differences among the Hartmann-Tran, quadratic-speed-dependent Voigt, and Voigt profiles. The temperature dependence of each line-shape parameter was further parameterized using the triplet-power-law for three pure rotational 61, 6 ← 52, 3, 41, 4 ← 32, 1, and 31, 3 ← 22, 0 lines. These line-shape parameters will provide a comprehensive set of theoretical references for subsequent experimental measurements.

Analysis of the He-, Ar- and Kr-broadening coefficients of water vapor transitions in a wide spectral region

An analysis of the measured He-, Ar- and Kr- broadening coefficients γ for 1575 water vapor transitions of 27 vibrational bands belonging to the 0.6-11,200 cm^-1 spectral region is performed using an empirical function that contains adjustable parameters. A universal function is detected during the analysis. This function depends on the parameters that are common for all perturbers A = (He, Ar or Kr). A universal function multiplied by one additional parameter x₂₀(A) determines the broadening coefficients γ(A) for each perturber A = (He, Ar or Kr).Two fitting procedures are used. The first considers the fit of measured γ(exp) for individual rotational branches while the other considers the global fit of all 1575 measured γ(exp). In the second procedure, ratios of γ(Kr)/γ(He) = 2.543 ± 0.040 and γ(Kr)/γ(Ar) = 1.252 ± 0.036 are found. The coefficients derived from the fitted parameters are compared statistically to measured coefficients.