HIGH RESOLUTION ABSORPTION COEFFICIENTS FOR DICHLORODITLUOROMETHANE AND THE TEMPERATURE DEPENDENCE OF THE $\nu6$ Q-BRANCH AT $1161 CM^{-1}$
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Date
1980
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Ohio State University
Abstract
Ultra high resolution absorption coefficients of dichlorodifluoromethane (CFM-12) have been obtained using tunable diode laser spectroscopy. Frequencies were measured relative to well known $SO_{2}$ lines using a 5 cm Germanium etalon. Self- and nitrogen-broadened absorption coefficients were studied as a function of pressure and temperature. Continuous spectra from $1150 cm^{-1}$ to $1173 cm^{-1}$ with a spectral resolution of $\sim 0.001$ $cm^{-1}$ are presented. The pure CFM-12 data, obtained at pressures between 25 and 300 millitorr, exhibited rich, highly structured spectra. For nitrogen pressures greater than 20 torr, collisional broadening reduces most of this spectral region to a structureless continuum. However, three features at $1158.2 cm^{-1}$, $1159.0 cm^{-1}$, and $1161.0 cm^{-1}$ remain isolated even at elevated nitrogen pressures. The two lower frequency features are attributed to hot band absorption and the $1161.0 cm^{-1}$ feature to the $\nu6$ fundamental absorption. The temperature dependence from 300K to 207K of the $1161.0 cm^{-1}$ feature supports the assignment as a fundamental band since the integrated absorption is inversely proportional to the absolute temperature. In the high resolution spectral data presented here, absorption due to the $CF_{2}{^{3}5}C\ell_{2}$ and $CF_{2}{^{3}5}C\ell^{37}C\ell$ isotopic species is well separated in all three major features. Although somewhat obscured in the room temperature spectra, the $CF_{2}{^{3}7}C\ell_{2}$ absorption becomes clearly visible at the lower temperatures studied.
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