Temperature dependence of the collision-induced absorption band of O2 near 1.27 µm

International audienceThe 1.27 µm O2 band is called upon to be used more and more for air-mass determination from ground-based and space-borne atmospheric spectra because of its advantages compared to the A-band at 0.76 µm. For this purpose, it is important to well characterize not only the narrow absorption lines but also the strong underlying broad collision-induced absorption (CIA) structure and its temperature dependence. Spectra of O2 and of O2 in N2 were recorded by cavity ring down spectroscopy (CRDS) at 271 K and 332 K, with the help of a newly developed temperature regulated cell. The quality of the spectra allowed determining the small variations (at the few percent level) of the, and binary coefficients with temperature. Together with the binary coefficients at 297 K reported previously, they allow characterizing the temperature dependence of the O2 CIA at 1.27 µm in atmospheric conditions. The obtained results are compared with previous measurements by Fourier transform spectroscopy (FTS) and recent theoretical calculations. In the wings of the pure O2 CIA, an increase with temperature is observed in agreement with calculations but contrary to the latter, a decrease is observed near the maximum of the CIA band. The temperature dependence is found in good agreementwith the theoretical values and the experimental values derived from the FTS measurements. Binary coefficients integrated over the entire band show almost no variation with temperature for O2-N2 and a small increase for pure O2, in agreement with the theoretical predictions