New transitions and energy levels of water vapor by high sensitivity CRDS near 1.73 and 1.54 µm

This contribution is part of a long term project aiming at improving the water absorption spectroscopy by high sensitivity cavity ring down spectroscopy (CRDS) in the near infrared. Two new sources of CRDS spectra are considered: (i) The room temperature absorption spectrum of water vapor in natural isotopic abundance is recorded near 1.73 µm. A series of recordings was performed from 5693 to 5991 cm−1 with a pressure value of about 6 Torr. The noise equivalent absorption (αmin) of the spectra is better than 10− 10 cm−1. A total of 1453 lines were assigned to 1573 transitions of four water isotopologues (H2 16O, H2 17O, H2 18O and HD16O). Their intensities span more than five orders of magnitude from 3.0 × 10−30 to 4.7 × 10−25 cm/molecule at 296 K. The assignments were performed using known experimental energy levels as well as calculated line lists based on the results of Schwenke and Partridge. Two hundred fifty-one lines (assigned to 280 transitions) are observed for the first time and twelve energy levels are newly determined. The comparison of the obtained line parameters with those of the HITRAN database is discussed. Forty-six line positions are observed to significantly differ from their HITRAN values (δν = │νHITRAN – νCRDS│ > 0.02 cm−1). The derived set of energy levels is compared to those recommended by an IUPAC task group. (ii) The room temperature CRDS spectrum of water vapor highly enriched in 17O was recorded near 1.54 µm (6223–6672 cm−1) at a pressure of 12 Torr. Compared to a previous study, the higher pressure of the recordings allowed for extending the observations. Overall, twenty-six new levels were determined for both H2 17O and HD17O. All these observations together with other recent measurements will allow for an extension and an update of our empirical database in the 5693– 8340 cm−1 region