Structural Transition in the OH(H₂O)_n Cluster in Water Vapors

S. V. Shevkunov

St. Petersburg State Technical University, Politekhnicheskaya ul 29, St. Petersburg, 195251 Russia

e-mail: root@svsh.tu.neva.ru

Received November 21, 2007

Abstract—The hydration of hydroxyl ion in water vapors at temperatures corresponding to seasonal variations
in natural air medium is studied by the Monte Carlo simulation in grand canonical statistical ensemble using
the detailed model of intermolecular forces that takes into account many-particle covalent interactions, polar-
ization, and charge transfer. An increase in the number of water molecules in a cluster is accompanied by a
structural transition from strongly asymmetric ion environment of water molecules to the formation of envel-
oping shell composed of these molecules. This transition is accompanied by an abrupt increase in cluster size
and qualitative changes in its structural characteristics. The displacement of ion on the surface of clusters with
extremely small sizes is an entropy effect. Results of simulation are compared with data on the hydration of
hydroxonium at which similar structural transition is not observed, and with data of quantum-chemical calcu-
lations.

DOI: 10.1134/S1061933X08060161

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