Continuum in the windows of the water vapor spectrum.: Absorption of H2O-Ar at 239 GHz and linewidth calculations

Absolute absorption rates of mixtures of water vapor and argon have been measured at 239 GHz, which is an atmospheric window for the rotational spectrum of water vapor. The dependence on pressure as well as temperature has been obtained. The experimental data are compared with models using conventional line profiles. As these models require the knowledge of the collisional linewidths of H2O broadened by Ar, theoretical calculations using the Robert-Bonamy formalism have been carried out. A continuum effect is observed when comparing the experimental absorption with the models, as well as for the magnitude of the absorption discrepancy and for the strong temperature dependence of this absorption. The effect, when compared to the collisional broadening efficiency, is about the same as that observed for H2O-N-2. (C) 1998 Elsevier Science Ltd. All rights reserved.