Temperature Dependence of the Collision-Induced Absorption Band of O₂ Near 1.27 µm

The 1.27 μm O₂ band is increasingly called upon for air-mass determination from ground-based and space-borne atmospheric spectra because of its spectral proximity to CO₂, and CH₄ bands at 1.6 μm, in contrast to the more distant 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 pure 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 (Formula presented.), (Formula presented.), and (Formula presented.) 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 O₂-O₂ CIA, an increase with temperature is observed in agreement with calculations but contrary to these calculations, a decrease is observed near the maximum of the CIA band. The temperature dependence is found in good agreement with the theoretical (Formula presented.) values and the experimental (Formula presented.) 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.