Comb-Assisted Cavity Ring Down Spectroscopy of 17O enriched water between 6667 and 7443 cm−1

Abstract

The room temperature absorption spectrum of water vapour highly enriched in 17O is studied by Comb Assisted-Cavity Ring Down Spectroscopy (CA-CRDS) near 1.4 µm. The investigated spectral region (6667–7443 cm−1) is a strong absorbing region corresponding to the first hexade of interacting vibrational states. As a consequence of the high sensitivity of the recordings (Noise Equivalent Absorption, αmin∼ 10−10 cm−1), a series of spectra could be recorded at very low pressure (less than 0.1 Torr) allowing for accurate determination of line centres and the spectral resolution of highly blended multiplets. For instance, 85 lines of the main isotopologue located near much stronger lines are measured for the first time. The assignments were performed using known experimental energy levels as well as calculated line lists based on the results of Schwenke and Partridge. Overall, the experimental list includes 9144 water lines which were assigned to 9988 transitions of six isotopologues (H2 16O, H2 17O, H2 18O, HD16O, HD17O and HD18O). Their intensities span six orders of magnitude from 10−27 to 10−21 cm/molecule at 296 K. Most of the new results concern the H2 17O isotopologue: more than 2300 new lines were measured, 64 new levels were determined and seven levels were corrected. In the case of HD17O, 152 new transitions were assigned and ten levels were newly determined. The center values of non-blended lines are reported with an accuracy better than 3 MHz (10−4 cm−1) which represents an improvement compared to previous determinations. The comparison to the water vapor line list provided by the recently released 2016 version of the HITRAN database reveals a number of issues. © 2017 Elsevier Ltd