| Water Dimer |
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The water dimer consists of two Water molecules loosely bound by a Hydrogen Bond . It is the smallest Water Cluster . Because it is the simplest model system for studying hydrogen bonding in water, it has been the target of so many theoretical (and later experimental) studies that it has been called "a theoretical Guinea pig" (Jeffrey, 1997). STRUCTURE AND PROPERTIES The binding energy between the two water molecules is estimated to be 5-6 kcal/mol, although values between 3 and 8 have been obtained depending on the method. The O-O distance is estimated at 1.98 Å; the hydrogen bond is almost linear, but the angle with the plane of the acceptor molecule is about 57°. These data are for the lowest energy configuration, known as the linear water dimer (shown in the figure above); other configurations of interest include the cyclic dimer and the bifurcated dimer. HISTORY The first theoretical study of the water dimer was an Ab Initio calculation published in 1968 by Morokuma and Pedersen. Since then, the water dimer has been the focus of sustained interest by theoretical chemists concerned with hydrogen bonding—a search of the CAS database up to 2006 returns over 1100 related references (73 of them in 2005). REFERENCES
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