A far wing line shape theory and its application to the water vibrational bands (II)

Abstract

A far wing line shape theory based on the binary collision and quasistatic approximations that is applicable for both the low and high frequency wings of vibration–rotational bands is presented. This theory is applied in order to calculate the frequency and temperature dependence of the continuous absorption coefficient for frequencies up to 10 000 cm−1 for pure water vapor. The calculations are made assuming an interaction potential consisting of an isotropic Lennard-Jones part with two parameters that are consistent with values obtained from virial data and the anisotropic dipole–dipole part, together with measured line strengths and positions of allowed transitions. The results are compared with existing laboratory data in the 2400–2700 cm−1 window and in the 3000–4300 cm−1 band center region, with field measurements in the 2000–2225 cm−1 region and with a recent experimental measurement near 9466 cm−1. The overall good agreement, together with even better agreement with the more accurate laboratory data in the 300–1100 cm−1 window presented previously, allows us to conclude that both the magnitude and temperature dependence of the water vapor continuum can be accounted for by our comprehensive far wing line shape theory without the introduction of any adjustable parameters. Refinements of the present theory and extension to foreign-broadened absorption are also discussed briefly.