Pressure broadening of water and carbon monoxide transitions by molecular hydrogen at high temperatures

Abstract

Water and carbon monoxide are two major compounds in the predominantly H2 atmospheres of stars, brown dwarfs and extrasolar planets. Recent radiative transfer models suggest that there is an urgent need for data on the pressure broadening of molecular transitions by H2 at high temperatures. We present a set of theoretical H2 pressure broadening parameters for 228H2O transitions in the range of 10–20,000GHz and 30 CO transitions in the 115–3500 GHz region. These parameters are appropriate for temperatures between 200 and 3000K. The random phase approximation is employed to derive the broadening parameters from recent state-of-the-art inelastic collisional rate coefficients. This approximation is compared both to full close-coupling calculations and to available experimental data. It is shown to be valid at temperatures above 200K, as expected from theoretical considerations, with an accuracy of about 25%.