Conditions and Mechanism of the Ionization and Dissociation of Water. Predictions Based on Nonempirical Calculations

Yu. V. Novakovskaya

Laboratory of Quantum Mechanics and Molecular Structure, Chair of Physical Chemistry,
Faculty of Chemistry, Moscow State University, Leninskie gory, Moscow, 119992 Russia

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Received October 12, 2006

Abstract — Based on the results of quantum chemical modeling of neutral and charged water clusters, mechanisms of the ionization and dissociation of water explaining the regularities discovered in experiments are proposed. There are two possible ways of the water and ice ionization, namely, (i) directly from the ground elec-tronic state of the neutral system provided that the high-frequency stretching vibrations of molecules, which determine the formation of H₃O⁺ and OH ionic fragments, are sufficiently excited, and (ii) via the intermediate transfer to the excited electronic state where hydronium radicals may appear at a certain excess energy. The formation of atomic hydrogen may also take place in the processes of two kinds, namely, (i) the dissociation of the electronically excited water clusters and (ii) the recombination of an electron, appeared upon ionization, with a hydronium cation that leads to the spontaneous detachment of a hydrogen atom. The processes may proceed either successively or simultaneously in a time period compared to the characteristic or even resolution time of the experiment, which may result in incorrect estimation of the quantum yields of hydrated electrons and hydrogen atoms in terms of standard procedures.

PACS numbers: 33.20.Lg; 33.20.Ni; 33.80.-b; 33.80.Rv

DOI: 10.1134/S0033173207030022