Water vapor absorption in the atmospheric window at 239 GHz

The Continuum of Water Vapor Mixed with Methane: Absolute Absorption at 239 GHz and Linewidth Calculations

“…(1), several review articles have been devoted to the subject, mainly for the infrared region (2)(3)(4)(5). In the mmw region a "continuum effect" is brought to the fore; it reveals an observed absorption higher than that predicted by models using lineshapes based upon the impact approximation; also pressure and temperature dependencies do not agree with the theoretical predictions.…”

“…As in the previous experiments (1,(15)(16)(17)(18), the pressure of the mixing gas, CH 4 , was fixed at 750 Torr. The purity of CH 4 was 99.995%.…”

“…Argon, a monoatomic gas, was also selected as a mixing gas (19). Both H 2 O-CO 2 and H 2 O-Ar mixtures presented a continuum effect of different magnitude, which gave rise, with our previous data (1,15,17), to the hypothesis of possible weakly bound complexes (20).…”

“…Our experimental data for pure water vapor and an atmospheric mixture of nitrogen have been compared with some of these models (1,(15)(16)(17) and have disclosed restrictions and limits on some calculated continuums. To get more insight on the molecular processes involved and in the aim of a more general treatment of the line profile, we have undertaken studies with other collisional partners.…”

“…The frequency has been chosen to be the same as that of our previous experiments (1,15,17), 239.370 GHz. This frequency is in a region where the excess absorption was shown to be the largest with respect to that predicted by current lineshapes.…”