Characterization of the H<SUB>2</SUB>O+CO<SUB>2</SUB> continuum within the infrared transparency windows

International audienceAbsorption spectra of humidified CO2 have been recorded at room temperature by cavity enhanced absorption techniques (CRDS and OFCEAS): (i) in three spectral ranges of the 1.6 μm window (5720-6045 cm-1; 6390-6460 cm-1 and 6570-6665 cm-1), (ii) in four narrow spectral intervals of the 2.3 μm window (4243-4255 cm-1; 4301.3-4302 cm-1; 4421.5-4440 cm-1 and 4518-4535 cm-1), and (iii) around 2853 cm-1. All these spectral ranges are situated in transparency windows of both H2O and CO2. The binary absorption coefficients (BCO2 -H2 O +BH2 O - CO2) are retrieved from low pressure spectra (2 after subtracting the H2O and CO2 local monomer contributions and the self-continuum contribution of each species (i.e. H2Osbnd H2O and CO2sbndCO2). Experimental room temperature binary coefficients are then compared to the only available empirical model based on line shape profiles with χ-factors. This model well reproduces our experimental values on the low- and high-frequency edges of the 1.6 μm window and gives a relatively good agreement for the 2853 cm-1 data point. Larger differences are observed in the 2.3 μm window where the calculated values are underestimated by a factor of 3. Around 6000 cm-1, an additional absorption peak is observed which is tentatively interpreted as a collision induced absorption band due to the simultaneous excitation of the H2O and CO2 molecules