Half-widths, their temperature dependence, and line shifts for the HDO–CO2 collision system for applications to CO2-rich planetary atmospheres

Measurements of water vapor in the atmospheres of Venus or Mars by spectroscopic techniques in the infrared range are being made routinely by instruments onboard the Venus Express and the Mars Reconnaissance Orbiter. The interpretation of these measurements in the 2250–4450 cm−1 region is being complicated by the presence of HDO lines absorbing radiation in this region. These spectra cannot be modeled properly because line shape parameters for CO2 broadening (principal gas in these atmospheres) of HDO are not available. Here semi-classical line shape calculations for the HDO–CO2 collision system are made using the Robert–Bonamy formalism for some 2300 rotational band transitions of HDO. From these calculations, the half-width, its temperature dependence, and the line shift are determined to aid in the reduction of the measured spectra. These data will greatly reduce the uncertainty of the reduced profiles from the Venus and Mars measurements and will also allow better estimates of the D/H ratio on these planets.