The far-infrared spectrum of 18O enriched water vapour (40-700 cm-1)

The rotational spectrum of water vapour highly enriched in 18 0 has been studied by high resolution (approximate to 0.001 cm(-1)) Fourier transform spectroscopy at the AILES beam line of the SOLEIL synchrotron. The room temperature absorption spectrum has been recorded between 40 and 700 cm(-1). The O-18 enrichment of the sample was about 97% while the gas pressure and the absorption pathlength were set to 0.97 mbar and 151.75 m, respectively. The spectrum contains more than 4800 rotational transitions from seven water isotopologues ((H2O)-O-18, (H2O)-O-16, (HDO)-O-17, (HDO)-O-18, (HDO)-O-16, (HDO)-O-17, (D2O)-O-18). The assignments were performed using known experimental energy levels as well as calculated line lists based on the results of Schwenke and Partridge. The amount and accuracy of the reported line positions represent an important extension compared to previous works. Overall, lines of about 2570 transitions are observed for the first time and 35, 41, 50, and 16 new energy levels are determined for (H2O)-O-18, (H2O)-O-17, (HDO)-O-18, and (HDO)-O-17, respectively. The set of derived energy levels shows a number of important differences from those recommended by an IUPAC-task group. Compared to the HITRAN2016 database, numerous deviations of line positions (up to 0.15 cm -1 ) are found for the (H2O)-O-17, (H2O)-O-18, (HDO)-O-17, and (HDO)-O-18 species. Incomplete and wrong HITRAN's assignments of more than 90 transitions for (H2O)-O-18, (H2O)-O-17 and (HDO)-O-18 are identified. Overall, the measured line positions will allow to significantly refine and complete the sets of empirical energy levels of (H2O)-O-18, H-2 O-17, (HDO)-O-18 and (HDO)-O-17 in the ground vibrational state. (C) 2020 Elsevier Ltd. All rights reserved.