Water dimer and the atmospheric continuum
The physical origin of humidity-related atmospheric continuum absorption is examined. The existence of double water molecules (dimers) in equilibrium water vapor at room temperature is proved by direct spectroscopic experiments supported by ab initio calculations. It is demonstrated that diluting water vapor with air does not significantly reduce the abundance of dimers. Numerous previous studies have predicted the presence of water dimers in the atmosphere and their influence on chemical reactions, homogeneous condensation, and Earth's radiation balance. Our results provide experimental proof of the presence of dimers in the atmosphere, thus enabling a detailed study of their role in natural processes. Prospects for future research are discussed.