The water vapor continuum absorption measured in moist nitrogen  at atmospheric pressure (c).
 M.A.Koshelev, E. A. Serov, V. V. Parshin, and M. Yu. Tretyakov, J. Quant. Spectrosc. Radiat. Transfer 112, 2704 (2011).
Water dimers (H2O)2 are believed to affect Earth’s radiation balance and climate, homogeneous condensation, and atmospheric chemistry. Moreover, the pairwise interaction which binds the dimer appears to be of paramount importance for expounding a complete molecular description of the liquid and solid phases of water. However, there have been no secure, direct observations of water dimers at environmentally relevant temperatures despite decades of studies. We report the first unambiguous observation of the dimer spectrum recorded in equilibrium water vapor at room temperature.
The paper presents results of extensive experimental study of the water related continuum absorption in a mixture of water vapor and nitrogen in 107–143 GHz frequency range at accurately controlled laboratory conditions. Resonator spectrometer and modified method of measurement that minimizes systematic errors related to water adsorption were employed. It allowed investigation in temperature range 261–328 K, including a first-time laboratory study of the continuum at temperatures below freezing. Coefficients of the common empirical parameterization of the continuum including self (H2O–H2O) and foreign (H2O–N2) parts are derived and compared with results of the most known previous experimental and theoretical studies demonstrating very good qualitative and in some cases quantitative agreement. Dominating types of intermolecular interactions leading to the observed continuum are discussed.