An improved line list for water vapor in the 1.5 µm transparency window by highly sensitive CRDS between 5852 and 6607 cm−1

Abstract

The absorption spectrum of water vapor in “natural” isotopic abundance has been recorded by high sensitivity Continuous Wave Cavity Ring Down Spectroscopy (CW-CRDS) between 5852 and 6607cm−1. The investigated region covers the 1.5µm transparency window of major importance for atmospheric applications. The achieved sensitivity of the recordings varies from αmin ∼2×10−11 to 2×10−10cm−1 and allows for a significant amount of new or more accurate observations compared to previous studies. Measured line intensities cover a range of six orders of magnitude (2×10−30−2×10−24cm/molecule at room temperature). The vibration–rotation assignments were performed using known experimental energy levels and calculated spectra based on variational calculations by Schwenke and Partridge.Five thousand seven hundred and twenty seven lines were assigned to 6379 transitions of six water isotopologues (H216O, H218O, H217O, HD16O, HD18O and HD17O). The first detection of lines due to HD17O in “natural” water (relative abundance on the order of 1.1×10−7) illustrates the sensitivity of the recordings. Most of the 1842 newly reported transitions belong to the main isotopologue (1022 transitions) and to the HD16O isotopologue (684 transitions). Sixty-three levels are newly determined and 22 are corrected by more than 0.015cm−1 compared to those recommended by the water IUPAC task group.Overall, a list of 6589 transitions was constructed for the studied region. The present CRDS line list complemented with 210 strong transitions from the literature is believed to be the most complete empirical list of the region. The obtained results are critically compared to recent IUPAC task group compilations. Overall the agreement between variational and measured intensities is very satisfactory. We nevertheless point out a number of important disagreements for some lines of the highly excited bending bands, mainly 4ν2 of H216O.