High sensitivity Cavity Ring Down spectroscopy of 18O enriched carbon dioxide between 5850 and 7000 cm−1: Part II—Analysis and theoretical modeling of the 12C18O2, 13C18O2 and 16O13C18O spectra

Abstract

More than 19000 transitions belonging to 11 isotopologues of carbon dioxide have been assigned in the room temperature absorption spectrum of highly 18O enriched carbon dioxide recorded by very high sensitivity CW-Cavity Ring Down spectroscopy between 5851 and 6990cm−1 (1.71–1.43μm). The line positions were determined with accuracy better than 1×10−3cm−1 while the absolute line intensities are reported with an uncertainty better than 10%. This second report is devoted to the analysis of the bands of three multiply substituted isotopologues: 12C18O2, 13C18O2 and 16O13C18O (828, 838 and 638 in short hand notation).On the basis of the predictions of effective Hamiltonian models, a total of 2870, 538 and 1375 transitions belonging to 59, 11 and 15 bands were rovibrationnally assigned for 828, 838 and 638, respectively. For comparison, only 11 bands were previously measured by Fourier Transform spectroscopy in the region, for the 828 species. All the identified bands correspond to a ΔP=9 variation of the polyad number (P=2V1+V2+3V3, where Vi are vibrational quantum numbers). The band-by-band analysis has allowed deriving accurate spectroscopic parameters of 81 bands from a fit of the measured line positions. A few resonance perturbations were identified. In particular, the 31113 and 51106 states of 638 belonging to different polyads (P=10 and P=11, respectively) are anharmonically coupled.Using the large set of newly measured line positions and those collected from the literature, the global modeling of the line positions within the effective Hamiltonian approach was performed and a new set of Hamiltonian parameters was obtained for each of the three considered isopotologues. Using a similar approach, the global fits of the obtained intensity values of the ΔP=9 series of transitions were used to derive the corresponding ΔP=9 effective dipole moment parameters of the three considered isotopologues. The obtained results will help to improve the quality of the spectral line parameters of the three considered minor isopotologues in the most currently used spectroscopic databases of carbon dioxide.