CLUSTERING OF WATER VAPOR ON IONS AND NEUTRAL MOLECULES

Abstract

Studies have been conducted in the University of Colorado laboratory to determine factors governing the stability and structure of clusters of water vapor on both ions and neutral molecules of atmospheric interest. Data on bonding involving a variety of negative and positive ions enable an assessment of the influence of temperature and water vapor partial pressure on ion cluster distributions. Semi-quantitative quantum mechanical calculations, in conjunction with the measurements, lend insight into cluster structure. Comparison of measured enthalpies and entropies with the classical liquid drop model reveal its shortcomings in predicting nucleation. In the case of neutral clusters, evidence has been obtained for the existence of a clathrate-like structure involving 21 water molecules stabilized by a mobile proton. Clustering of water to neutral acid molecules has been found to lead to the formation of an electrolytic micro-droplet with very few water molecules. The role of these various cluster species in condensation phenomena and as prenucleation embryos to gas-to-particle conversion is discussed.