High sensitivity (femto-FT-CEAS) spectra of carbonyl sulphide between 6200 and 8200 cm−1, and new energy pattern in the global rovibrational analysis of 16O12C32S

- Very weak bands in OCS are reported and analysed between 6170 and 8160 cm−1.
- The full vibration-rotation literature data on OCS is gathered and made available.
- All these data are precisely accounted for updating the global rovibrational model.
- This model includes two inter-polyad interactions, of anharmonic and Coriolis type.
- We have generated predictions of rovibrational state parameters up to 15,000 cm−1.

We have recorded Fourier transform spectra of OCS between 6170 and 6680 cm−1, and between 7700 and 8160 cm−1 using a femto/OPO laser absorption source and cavity enhanced spectroscopy. Equivalent absorption path lengths varying between 7 and 13 km were obtained depending on the specific spectral region. In the lower and higher energy ranges, 7 and 12 new bands were observed, respectively, while improved results were gained on those previously reported in the literature. Some of these data brought significant, new information on the rovibrational energy pattern in OCS that triggered an update of the latest published global polyad model (Rbaihi et al. J Mol Spectrosc 1998;191:32 [15]). The new fit includes for the first time all overtone data since published in the literature, covering the range 6200-13950 cm−1, as well as all known lower energy ones. All data selected for the global analysis of carbonyl sulphide 16O12C32S are provided as supplementary information.The previous polyad model was extended to include the inter-polyad anharmonic k1113 and Coriolis C11222 interactions, leading to simultaneously deal with sets of nine interacting polyad matrices at a time, each polyad defined by N=2v1+v2+4v3 (with 1-3 the conventional normal modes in OCS). We have obtained a statistical agreement with all experimental data with an estimated standard deviation better than unity (σ^=0.7568). The fit produced 141 molecular parameters, of which 4 concern the new inter-polyad resonances. They have been used to calculate effective rovibrational parameters for all sub-states up to more than 12,000 cm−1, listed in a Depository (Appendix B). A list of line parameters, covering the measured spectral ranges and including line intensities determined using previously recorded Fourier transform spectra of the two strongest bands observed in the present work, was generated in HITRAN format. It is also provided as supplementary information.