Knowledge Bank

Ultra high resolution absorption coefficients of dichlorodifluoromethane (CFM-12) have been obtained using tunable diode laser spectroscopy. Frequencies were measured relative to well known $SO2$ 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 $1150cm-1$ to $1173cm-1$ 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 $1158.2cm-1$, $1159.0cm-1$, and $1161.0cm-1$ remain isolated even at elevated nitrogen pressures. The two lower frequency features are attributed to hot band absorption and the $1161.0cm-1$ feature to the $\nu 6$ fundamental absorption. The temperature dependence from 300K to 207K of the $1161.0cm-1$ 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 $CF2\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}5C\ell 2$ and $CF2\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}5C\ell 37C\ell$ isotopic species is well separated in all three major features. Although somewhat obscured in the room temperature spectra, the $CF2\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}7C\ell 2$ absorption becomes clearly visible at the lower temperatures studied.