On the possibility to quantify contributions from true bound and metastable pairs to infrared absorption in pressurised water vapour

The present paper aims to evaluate the proportions of true bound and metastable water dimers from an analysis of laboratory observations of the integrated absorption in the OH stretching band of pressurised water vapour. Knowledge of the statistical weights of true bound and metastable dimers is of crucial importance for understanding the nature of bimolecular absorption by water vapour. It is particularly relevant for understanding the nature of the so-called water vapour continuum absorption in the atmosphere, the cause of which has been debated over many decades. Our consideration is essentially based on the recent laboratory measurements of water dimer spectroscopy data as well as independent measurements of the density variations in absorptivity of pressurised steam.