CRDS of water vapor at 0.1 Torr between 6886 and 7406 cm−1

The absorption spectrum of water vapor in “natural” isotopic abundance has been recorded by high sensitivity CW-Cavity Ring Down Spectroscopy (CW-CRDS) between 6885.79 and 7405.91 cm−1. This strong absorbing region includes the first hexad of interacting vibrational bands which was previously studied by Fourier Transform Spectroscopy. The achieved sensitivity of the recordings varies from αmin∼2×10-11 to 2×10−10 cm−1 allowing us to use a sample pressure of 0.1 Torr, making pressure broadening of the line profile mostly negligible. Weak lines in the vicinity of much stronger lines could then be accurately measured. The weakest lines have intensity on the order of 5×10-28 cm/molecule at 296 K. A set of 4471 lines were assigned to 4916 transitions of five water isotopologues (H2 16O, H2 18O, H2 17O, HD16O and HD18O). A small number of new energy levels was determined mostly for the H2 17O isotopologue. The previous investigations and existing databases are critically evaluated. In particular, a number of corrections and new assignments are proposed for the water list provided by the HITRAN database in the considered region. As a result, a complete list of 12,700 transitions for water in “natural” isotopic abundance is provided as Supplementary Material for the 6885-7408 cm−1 region.

► High sensitivity cavity ring down spectra of water vapor between 6886 and 7406 cm−1. ► 4471 lines assigned to 4916 transitions of H2 16O, H2 18O, H2 17O, HD16O, and HD18O. ► 1277 weak water transitions detected for the first time. ► Critical evaluation of the HITRAN line list in the region. ► Construction of a complete list for water (intensity cut off of 10−28 cm/molecule).