The absorption spectrum of water in the 1.25 μm transparency window (7408–7920 cm −1)

Abstract

The absorption spectrum of water vapor in “natural” isotopic abundance has been recorded between 7408 and 7920 cm −1 by high sensitivity cw-cavity ring down spectroscopy (CW-CRDS). This region covers the low energy part of the 1.25 μm transparency window and corresponds to weak water absorption of the first hexad of interacting vibrational bands. The achieved sensitivity – on the order of α min ∼ 2 × 10 −10 cm −1 – has allowed one to newly measure 2028 weak transitions with intensities down to 2 × 10 −29 cm/molecule at 296 K i.e. more than two orders of magnitude lower than previous observations. Three hundred and fourty-one new and corrected energy levels belonging to 26 vibrational states of H 2 16O, H 2 18O, H 2 17O, and HD 16O could be determined from the vibration–rotation analysis based on variational calculations by Schwenke and Partridge. The previous investigations in the studied region by Fourier Transform Spectroscopy and existing databases have been critically evaluated. The most complete list for water in the region is provided as Supplementary Material.