Absorption of a H2O–CO2Mixture in the Atmospheric Window at 239 GHz; H2O–CO2Linewidths and Continuum

Abstract Absolute absorption rates of mixtures of water vapor and carbon dioxide have been measured at 239 GHz which is in an atmospheric window for the rotational and vibrational spectra of both species. The dependence on pressure as well as temperature has been obtained. The experimental data are compared with models using conventional lineshapes. As these models require the knowledge of the collisional linewidths of the H 2 O broadened by CO 2 , theoretical calculations using the Robert–Bonamy formalism have been carried out. A very large “continuum effect” is observed when comparing the experimental absorption with the models, as well for the magnitude of the absorption discrepancy and for the strong temperature dependence of this absorption. Collision induced absorption (CIA) has also been measured at this frequency. These results can be applied to planetary observations.