Air-broadened line parameters with temperature dependence for 12C16O, 13C16O, and 12C18O at 2.3 μm

To improve the spectroscopic database for remote sensing of tropospheric CO, we have recorded more than 50 high resolution (0.005 cm^-1) spectra of CO and two of its isotopologues (¹³CO and C¹⁸O) at temperatures between 150 and 298 K using a coolable absorption cell in the sample compartment of the Bruker IFS 125HR Fourier transform spectrometer at Jet Propulsion Laboratory. Air-broadened spectra at total pressures up to 700 Torr were recorded for all three isotopologues, and self-broadened CO spectra were also recorded. Line parameters were determined by broad-band constrained multispectrum least-squares fitting of 16 or more spectra simultaneously. Parameters determined in the fits included Lorentz half-width coefficients, their temperature dependence exponents; pressure-induced line shift coefficients, their temperature dependences; and the off-diagonal relaxation matrix elements that characterize line mixing. Speed dependence parameters were also included to minimize the fit residuals. The individual line positions and intensities were constrained to their theoretical relationships in order to obtain the rovibrational (G, B, D, and H) and band intensity parameters, including Herman-Wallis coefficients, as has been done for CO₂ previously. The air-broadening results for the ¹³C¹⁶O and ¹²C¹⁸O 2-0 bands are compared with each other and with those for the corresponding ¹²C¹⁶O band.