The water vapor self-continuum absorption at room temperature in the 1.25 µm window

Abstract

The water vapor self-continuum is newly measured at room temperature in the high energy edge of the 1.25 µm window by using highly stable and sensitive cavity ring down spectroscopy (CRDS). Self-continuum cross-sections, CS, are derived between 8290 and 8620 cm−1 at 29 selected spectral points by using pressure ramps (up to 15 Torr) of pure water vapor. Purely quadratic pressure dependence is obtained for the absorption coefficient at each measurement point. Although the spectral measurement points were chosen to minimize the contribution of resonance line absorption, the latter represents between 30 and 70% of the measured absorption in the studied region. The measurements are found consistent with a previous study of the low frequency edge of the 1.25 µm windows and (Campargue et al. J Geophys Res Atmos 2016;121:13,180 – 13,203. doi:10.1002/2016JD025531). The frequency dependence of the retrieved CS values shows an overall good agreement with the MT_CKD values, although an additional broad absorption feature is observed with a center near 8455 cm−1. It is tentatively interpreted as a possible impact of the uncertainties on the resonance line contribution on the derived CS values or as a possible evidence of a band of the bound dimers, (H2O)2.