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Updated: Jun 14, 2026

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
Published on: April 8, 2020
Infrared water vapor continuum absorption: equilibria of ions and neutral water clusters
Abstract:
The temperature dependence of (C(o)(s))lambda, the self-broadening coefficient for the water vapor continuum absorption at wavelength lambda, can be modeled by the equilibrium ion product of water which is tabulated widely in physics texts and handbooks. A theoretical basis for this modeling is developed from water cluster theory, and it is shown that experimental values of (C(o)(s))lambda. could be seriously in error, especially at high temperatures, if the saturation ratio (fractional RH) of water vapor is not taken into account by the experimenter for reasons other than normalization of the coefficient for partial pressure of the sample. An explanation is suggested for the departure of (C(o)(s))lambda from the usual negative dependence on increasing water vapor temperature in some experiments. Figures are given showing equilibrium sizes and populations of neutral water clusters and ions in water vapor as functions of humidity and temperature, based in part on data of Bignell and other workers.
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