Measurements and calculations of air-broadening and shift parameters of water vapour transitions in a wide spectral region

Abstract

The water vapour line broadening (γ) and shifting (δ) coefficients for 212 lines of eight vibrational bands, namely, ν 2 + ν 3, 2ν 2 + ν 3, 3ν 2 + ν 3–ν 2, 4ν 2, ν 1 + ν 3, ν 1 + ν 2, ν 1 + 2ν 2 and 2ν 1, in the 5800–6700 cm–1 spectral region induced by air are measured using Fourier transform infrared spectroscopy. The measurements are performed with a spectral resolution of 0.01 cm–1 and in a wide pressure range of air. The calculations of δ are based on the Anderson–Tsao–Curnutte theory. The measured γ values are combined with literature data for the half-widths found for the lines in the 380–14,000 cm–1 spectral region. The combined experimental data for N = 1386 measured γ coefficients of 17 vibrational bands of the H2O molecule perturbed by air are fitted to an empirical function. Two fitting procedures are used, with one considering the fit of the measured γ for individual rotational branches and the other considering the global fit of all 1386 measured γ. The computed γ values derived from the fitted parameters are compared statistically to the measurements. The vibrational dependence of the measured γ and their compatibility are discussed. The obtained fitted parameters of the empirical function are used for the analysis of γ for the lines in the 13,000 to 26,000 cm–1 spectral region.