The thermal infrared spectrum of water vapor beyond 8 pm consists of a fairly well-understood spectrum of rotational lines and an inadequately described continuum spectrum underlying the observed spectral lines. The contribution of the continuum absorption can be important in the calculations of the atmospheric radiative heating rates and of the net surface flux. This paper presents some new results on the continuum absorption in the thermal infrared between 8 and 18 μm along with a brief review of currently adapted empirical and semi-empirical models explaining its nature.
"Infrared Absorption By Water Vapor In The Atmospheric Window", Proc. SPIE 0928, Modeling of the Atmosphere, (24 August 1988); doi: 10.1117/12.975629; https://doi.org/10.1117/12.975629