Mass spectrometry was used to study ion-induced water clusters [H+(H2O)c], where c = the cluster size, i.e.,the number of monomers per cluster. It is shown that the numbers of hydrogen bonds in populations of these clusters in water vapor vary as the square of partial pressure and inversely with temperature, with functional dependencies that are almost identical to those observed for the infrared continuum absorption and for anomalous absorption in other wavelength regions. Experimental mass spectra taken at constant temperature vs partial pressure and data obtained at constant water vapor partial pressure vs temperature are presented and discussed. These results are combined with the evidence of cloud physicists including C. T. R. Wilson to show rather conclusively that naturally occurring ionic processes in water vapor generate large populations of hydrogen-bonded neutral water clusters that are responsible for the infrared continuum absorption. These processes can be enhanced by various kinds of ionizing energy, thus increasing anomalous absorption in water vapor or in moist air. If electrical properties of the atmosphere influence the infrared continuum absorption, which is an important mechanism in determining climate at the earth’s surface, it will be necessary to reexamine extensively existing models of atmospheric radiative transfer.
Hugh R. Carlon and Charles S. Harden, "Mass spectrometry of ion-induced water clusters: an explanation of the infrared continuum absorption," Appl. Opt. 19, 1776-1786 (1980)