CW-Cavity Ring Down Spectroscopy of 18O 3. Part 3: Analysis of the 6490–6900 cm −1 region and overview comparison with the 16O 3 main isotopologue

Abstract

This paper is devoted to the third part of the analysis of the very weak absorption spectrum of the 18O 3 isotopologue of ozone recorded by CW-Cavity Ring Down Spectroscopy between 5930 and 6900 cm −1. In the two first parts [A. Campargue, A. Liu, S. Kassi, D. Romanini, M.-R. De Backer-Barilly, A. Barbe, E. Starikova, S.A. Tashkun, Vl.G. Tyuterev, J. Mol. Spectrosc. (2009), doi: 10.1016/j.jms.2009.02.012 and E. Starikova, M.-R. De Backer-Barilly, A. Barbe, Vl.G. Tyuterev, A. Campargue, A.W.Liu, S. Kassi, J. Mol. Spectrosc. (2009) doi: 10.1016/j.jms.2009.03.013], the effective operators approach was used to model the spectrum in the 6200–6400 and 5930–6080 cm −1 regions, respectively. The analysis of the whole investigated region is completed by the present investigation of the 6490–6900 cm −1 upper range. Three sets of interacting states have been treated separately. The first one falls in the 6490–6700 cm −1 region, where 1555 rovibrational transitions were assigned to three A-type bands: 3 ν 2 + 5 ν 3, 5 ν 1 + ν 2 + ν 3 and 2 ν 1 + 3 ν 2 + 3 ν 3 and one B-type band: ν 1 + 3 ν 2 + 4 ν 3. The corresponding line positions were reproduced with an rms deviation of 18.4 × 10 −3 cm −1 by using an effective Hamiltonian (EH) model involving eight vibrational states coupled by resonance interactions. In the highest spectral region – 6700–6900 cm −1 – 389 and 183 transitions have been assigned to the ν 1 + 2 ν 2 + 5 ν 3 and 4 ν 1 + 3 ν 2 + ν 3 A-type bands, respectively. These very weak bands correspond to the most excited upper vibrational states observed so far in ozone. The line positions of the ν 1 + 2 ν 2 + 5 ν 3 band were reproduced with an rms deviation of 7.3 × 10 −3 cm −1 by using an EH involving the {(054), (026), (125)} interacting states. The coupling of the (431) upper state with the (502) dark state was needed to account for the observed line positions of the 4 ν 1 + 3 ν 2 + ν 3 band ( rms = 5.7 × 10 −3 cm −1). The dipole transition moment parameters were determined for the different observed bands. The obtained set of parameters and the experimentally determined energy levels were used to generate a complete line list provided as Supplementary Materials. The results of the analyses of the whole 5930–6900 cm −1 spectral region were gathered and used for a comparison of the band centres to their calculated values. The agreement achieved for both 18O 3 and 16O 3 (average difference on the order of 1 cm −1) indicates that the used potential energy surface provides accurate predictions up to a vibrational excitation approaching 80% of the dissociation energy. The comparison of the 18O 3 and 16O 3 band intensities is also discussed, opening a field of questions concerning the variation of the dipole moments and resonance intensity borrowing by isotopic substitution.