CW-Cavity Ring Down Spectroscopy of deuterated water in the 1.58 μm atmospheric transparency window

Abstract

The spectrum of water vapour enriched in deuterium has been recorded by highly sensitive CW-Cavity Ring Down Spectroscopy in the 5855–6802cm−1 spectral region. The studied region includes the 1.58µm atmospheric transparency window of particular interest for remote sensing. More than 8000 absorption lines belonging to eight water isotopologues – H216O, H218O HD16O, D216O, HD18O, D218O, HD17O and D217O – were identified.The spectrum was assigned using both the IUPAC database of experimental transitions and energy levels, and accurate variational calculations. Overall, 1396 and 1277 experimental energy levels belonging to 18 and 16 upper vibrational states were retrieved for the HD16O and D216O species, respectively. 773 energy levels are newly derived. New experimental information concerns the high J (up to 20) and high Ka (up to 12) energy levels of the (101), (021), (040), (210), (120) states of HD16O and of the (111), (031), (210), (012), (130) states of D216O. While only a few energy levels were available, the rotational structure of the (130) and (220) states of HD16O could be analysed in detail. Rotational sublevels of the (140) state of D216O are reported for the first time. A detailed comparison of the derived energy levels with the values recommended by an IUPAC task group is presented. In particular, a significant improvement is evidenced for a number of quasi degenerate energy levels of HD16O. The obtained results are also discussed in relation with several recent studies.