Measurements and modeling of absorption by CO₂+ H₂O mixtures in the spectral region beyond the CO₂ ν₃-band head

In this work, we measured the absorption by CO₂+ H₂O mixtures from 2400 to 2600 cm⁻¹ which corresponds to the spectral region beyond the ν₃ band head of CO₂. Transmission spectra of CO₂ mixed with water vapor were recorded with a high-resolution Fourier-transform spectrometer for various pressure, temperature and concentration conditions. The continuum absorption by CO₂ due to the presence of water vapor was determined by subtracting from measured spectra the contribution of local lines of both species, that of the continuum of pure CO₂ as well as of the self- and CO₂-continua of water vapor induced by the H₂O-H₂O and H₂O-CO₂ interactions. The obtained results are in very good agreement with the unique previous measurement (in a narrower spectral range). They confirm that the H₂O-continuum of CO₂ is significantly larger than that observed for pure CO₂. This continuum thus must be taken into account in radiative transfer calculations for media involving CO₂+ H₂O mixture. An empirical model, using sub-Lorentzian line shapes based on some temperature-dependent correction factors χ is proposed which enables an accurate description of the experimental results.