A balloon-borne spectrometer was used to measure the atmospheric absorption of solar radiation in the 9–10-µ region as a function of altitude. Among the numerous spectra recorded, several were made with very long optical paths above the troposphere obtained from floating altitude (~30 km) while the sun set. When the experimental results are compared with calculated spectra, based on line by line parameters of the ν3 and ν1 fundamentals of ordinary ozone, 16O3, combined with the Curtis-Godson approximation, large discrepancies are found for the long path spectra. It is shown that the hot bands ν3, + ν2, — ν2, and ν3, + ν3, — ν3, of the 16O3, and the ν3 fundamentals of the isotopic species 16O18O16O and 16O16O18O, can contribute significant absorption for long paths such as obtained in this experiment. Such long paths also give rise to significant absorptions by the ν3 - ν1 and the ν3 - 2ν2° bands of CO2. Including these weak bands in the calculated spectra leads to good agreement with the observed data.
A. Goldman, T. G. Kyle, D. G. Murcray, F. H. Murcray, and W. J. Williams, "Long Path Atmospheric Ozone Absorption in the 9–10-µ Region Observed from a Balloon-Borne Spectrometer," Appl. Opt. 9, 565-580 (1970)