Temperature Dependence of O ₂ Collision‐Induced Absorption Near 1.06 μm Measured by Cavity Ring‐Down Spectroscopy

Abstract

Oxygen collision‐induced absorption (CIA) near is extremely weak, yet accurate spectroscopic data for this band are important for atmospheric radiative‐transfer modeling and the interpretation of oxygen‐rich planetary atmospheres. This spectral region contains narrow O ₂ monomer absorption lines arising from the transition, superimposed on broad oxygen CIA. In this work, cavity ring‐down spectroscopy was used to measure O ₂ –O ₂ CIA over 9120– at 273, 303, and 333 K under low‐density conditions . The three pressure data sets recorded at 303 K gave mutually consistent spectra, with deviations mostly below 0.3% within the FWHM range of 9301–. Linear fitting of the values at the three temperatures yielded temperature‐dependence coefficients, , which are predominantly positive and indicate an overall enhancement of O ₂ –O ₂ CIA in this band with increasing temperature. Comparison with the ab initio data shows that both experiment and theory predict a positive temperature dependence. However, over the common integration interval of 9120–, the experimental temperature‐dependence coefficient of the integrated band intensity, , is , smaller than the theoretical value of . These results provide new experimental constraints on the temperature dependence of O ₂ –O ₂ CIA near and support the evaluation and refinement of theoretical descriptions of this band.