Evidence for the contribution of water dimers to the near-IR water vapour self-continuum

The nature of the water vapour continuum absorption and the possible contribution of water dimers (WD) to this phenomenon have been a matter of debate for many years. The current work presents an overview and analysis of a number of experiments, both recent and old, where spectral signatures, similar to recent theoretical predictions for WD, have been observed in equilibrium laboratory conditions within near-infra-red (IR) water vapour absorption bands. These experiments, in contrast to those where water complexes are usually studied in non-equilibrium and low-temperature conditions, can give direct information about the possible WD amount in atmospheric conditions. Intercomparison of the results of these works and the recent ab initio prediction for WD band intensities and positions testifies in favour of a significant contribution of WD absorption to the water vapour self-continuum in the centre of the strongest near-IR water vapour absorption bands.