Empirical energy levels and line lists of D217O, and D218O from the analysis of far infrared absorption spectra (50–720 cm-1)

This contribution is part of a long-term project aiming at improving our knowledge of the energy levels of the nine stable isotopologues of water vapor (H₂^XO, HD^XO, D₂^XO with X = 16, 17, and 18) from the analysis of their far infrared (FIR) spectra. The Fourier transform spectra were recorded with unprecedented sensitivity at the SOLEIL synchrotron facility. In a recent work (S. N. Mikhailenko, A. O. Koroleva, A. Campargue J. Phys. Chem. Ref. Data 54, 023,103 (2025) https://doi.org/10.1063/5.0273106), the analysis of five absorption spectra of water vapor highly enriched in ¹⁷O, ¹⁸O and deuterium (D) have allowed a significant extension of the observations for the HD¹⁷O and HD¹⁸O minor isotopologues. It turns out that the D₂¹⁷O and D₂¹⁸O partial pressures in these spectra (up to about 0.38 mbar and 0.27 mbar, respectively) were about one order of magnitude higher than those in the SOLEIL spectra dedicated to the D₂O species (S. N. Mikhailenko, E. V. Karlovets, A. O. Koroleva, and A. Campargue J. Phys. Chem. Ref. Data 53, 023,102 (2024) https://doi.org/10.1063/5.0202355). As a result, 548 and 380 transitions are newly measured for D₂¹⁷O and D₂¹⁸O, respectively, leading to the new determination of 147 and 59 energy levels, respectively. For each of the two species, the set of measured transition frequencies was merged to literature sources to generate extensive sets of accurate empirical rotational-vibrational energies for the ground, (000), and first excited, (010), vibrational states. Based on these accurate energy levels, recommended lists of transitions are generated with a 10^–26 cm/molecule intensity cut-off for the (000) – (000), and (010) – (010) rotational bands and the ν₂ fundamental band of D₂¹⁷O and D₂¹⁸O. For the microwave region (0 – 1.5 THz), more complete lists with an intensity cut-off lowered to 10^–29 cm/molecule are provided.