Ratio between Monomer and Dimer Absorption in Water Vapor within the H2O Rotational Band

Abstract

Spectral line shape derived using the asymptotic line wing theory (ALWT) with parameters obtained from fitting to experiment in the 8–12-μm spectral region, which describes the spectral and temperature behavior of water vapor absorption in this region, is used to calculate absorption in the longwave wing of the H₂O rotational band. The absorption coefficient calculated with the ALWT takes into account absorption by any colliding molecular pairs, except for the absorption due to stable dimers. Application of this line shape to calculation of the absorption coefficient in the region 14–200 cm⁻¹ allows us to extract the stable dimer absorption from the absorption measured with a special-resonator spectrometer. The dimer absorption spectrum derived shows consistency with the spectra from quantum-mechanical calculations and spectra measured in other experiments.