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Application of Computer-Simulated Infrared Solar Spectra to the Detection of Atmospheric Fluorocarbon-12

Volume 31, Number 3 (June 1977) Page 224-229

Nordstrom, Robert J.; Shaw, John H.; Skinner, Wilbert R.; Chan, Walter H.; Calvert, Jack G.; Uselman, William M.


Fluorocarbon-12 (CCl2F2) has been detected in the atmosphere by observation of infrared solar spectra in two spectral regions of the 8 to 12 μm atmospheric transmission window. The solar spectra were compared with laboratory spectra of CCl2F2 and also with computer synthesized spectra which were generated from the most recent Air Force Cambridge Research Laboratories line parameters listing. Water vapor lines interfere with strong Q-branch absorption features of CCl2F2 in the spectral region near 923 cm−1. The region near 1161 cm−1 is free from water vapor absorption and has the strongest Q-branch feature of CCl2F2. Many laboratory spectra of CCl2F2 were studied and this absorption feature was found to be independent of N2 broadening pressure. No change in the half-width was found as the N2 pressure was varied from 0 to 700 Torr. Furthermore, assuming a Lorentz line shape for this CCl2F2 absorption feature, an intensity of 3.8 × 10−18 cm. molecule−1 and a half-width of 0.026 cm−1 were found. Using these parameters, synthetic solar spectra were computed which included the CCl2F2 absorption feature. Results of this computer generation of solar spectra indicate a ground level concentration of 110 parts per trillion of CCl2F2 in our solar spectra.