Measurements and modeling of 16O12C17O spectroscopic parameters at 2 µm

Abstract

The lack of spectroscopic measurements for rare CO2 isotopologues was the main motivation of this work. In our present study we report line intensity measurements for 16O12C17O made with a high resolution Fourier transform spectrometer (Bruker IFS-125HR) and a 21 m path cryogenic Herriott cell at Jet Propulsion Laboratory. For this, a 17O-enriched CO2 gas sample was used, which comes as a mixture of primary and several minor CO2 isotopologues. The mole fraction of the 16O12C17O isotopologue in the mixture was determined to be 0.3991 by mass spectrometry from a Stable Isotope Ratio Mass Spectrometer (SIRMS) under stochastic distribution assumption at thermal equilibrium. Since the collisional narrowing effect was observed, the Rautian molecular line shape profile was systematically adopted instead of the Voigt profile. Absolute line positions were also investigated by performing a wavenumber calibration based on CO, HCl and a few well-known 16O12C16O transitions. Finally, around 1000 transitions were studied between 4604 and 5126cm−1 involving 15 bands of the 16O12C17O isotopologue. All the measured line intensities were renormalized to be the values for 100% pure isotopologue sample. Transition dipole moments and Herman-Wallis factors were derived enabling a global comparison with theoretical calculations and predictions for the 15 bands of the 16O12C17O isotopologue. For the measured line positions, the absolute accuracy is around 2×10−4cm−1. The accuracies of retrieved line intensities are 2 – 5% for five cold and two hot bands, and 6–30% for eight other weaker hot bands. Results from this work were in a good agreement with HITRAN 2012 for positions, but showed rather significant discrepancies for line intensities. An extensive line list was generated from new experimental measurements in order to improve and validate spectroscopic knowledge of 12C16O17O isotopologue in support of atmospheric remote sensing for the Earth (e.g., OCO-2 mission), Mars and Venus.