Positions, intensities and line shape parameters for the 1←0 bands of CO isotopologues

Abstract

Positions and intensities for transitions in the 1←0 bands of the four CO isotopologues (12C16O, 13C16O, 12C18O and 13C18O) were retrieved from analyses of spectra of different low-pressure pure samples and high-pressure air-broadened mixtures (1940–2260 cm−1) in two different multispectrum fittings involving selected groups of 21 (for 13C16O) and 20 (for 12C18O) spectra. Air-broadened half-width and air-shift coefficients, their temperature dependences, line mixing via off-diagonal relaxation matrix element coefficients for CO-air collision systems, and quadratic speed dependence parameters were measured for 13C16O and 12C18O transitions. In both the fittings, two low-pressure room-temperature spectra of a high purity natural sample of CO recorded with the Kitt Peak FTS were included to retrieve the positions and intensities of 12C16O transitions. All other spectra in the fittings were obtained with either 13C-enriched or 18O-enriched samples using the JPL Bruker IFS-125HR FTS. Four absorption cells with path lengths between 0.5131(5) and 20.38(2) cm were used to record the data. The cells are temperature controlled, except for the shortest cell. Positions and intensities for the 1←0 band transitions were determined from the retrieved ro-vibrational constants (G, B, D and H), band intensity and Herman-Wallis parameters by applying the theoretical quantum mechanical expressions. The band strengths of 12C16O, 12C18O and 13C18O are very close (∼0.3%) to HITRAN2012 values but for 13C16O the band strength is ∼4.8% larger than the HITRAN2012 and 2.6% larger than the HITRAN2016 value.