Knowledge Bank

The $791cm-1$ Q branch of $CO2$ will be used by the CLAES (Cryogenic Limb Array Etalon Spectrometer) instrument on UARS (Upper Atmosphere Research Satellite) for stratospheric temperature sounding. We have measured the strengths of a number of lines in the Q and R branches of this band using a tunable diode laser spectrometer. The line strengths are derived from the spectra using a modified equivalent width method that minimizes uncertainties in the 100% transmission background. Our results are compared to recent measurements of this band by Dana $et.al.1$ Spectra of this Q branch with total pressures between 100 and 740 torr, both self- and $N2$-broadened, were also recorded. We find excellent agreement between experiment and calculation for the self-broadened spectra using a simple energy gap scaling law to determine the off-diagonal collisional relaxation matrix. Although our calculations account for most of the line mixing in the $N2$-broadened spectra, we systematically underestimate the amount of line mixing by a small amount. This behavior has also been seen in other $CO2$ Q branches, both in the laboratory and in atmospheric spectra. The ramification of this disagreement for the energy gap scaling law used in this work will be discussed.