SELF- AND AIR-BROADENING OF $^{12}$C$^{16}$O, $^{13}$C$^{16}$O AND $^{12}$C$^{18}$O AT 2.3 $\mu$m

Abstract

High resolution (0.005 cm$^{-1}$) absorption spectra of CO and two of its isotopologues ($^{13}$CO and C$^{18}$O) were recorded between 3550 and 5250 cm$^{-1}$ using the Bruker IFS-125HR Fourier transform spectrometer (FTS) located at the Jet Propulsion Laboratory (JPL) and a specially designed and built coolable 20.38 cm long absorption cell nderline{\textbf{262}} (2010) 122-134.} placed within the sample compartment of the FTS. More than 50 spectra of both pure and air-broadened samples of CO, $^{13}$CO and C$^{18}$O were recorded at various temperatures from 150 K to 298 K, with maximum total pressures up to $\sim$700 Torr. A multispectrum nonlinear least squares spectrum fitting technique nderline{\textbf{53}} (1995) 705-721.} was used to determine the spectral line shape parameters including speed dependence, Lorentz halfwidth coefficients, pressure-induced shift coefficients, and off-diagonal relaxation matrix element coefficients for line mixing. These line shape parameters were obtained for both self- and air-broadening, and temperature dependences of these parameters were determined where possible. As previously done in studies of CO$_2$, nderline{\textbf{242}} (2007) 90-117.} rather than retrieving individual line positions and intensities, we constrained them to their theoretical relationships, including Herman-Wallis terms, determining only the band intensities and rovibrational constants. The results are discussed and compared with values reported in the literature.