Theoretical Estimation of the Ionization Potential of Water in Condensed Phase. II. Superficial Water Layers

Yu. V. Novakovskaya

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

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Received May 7, 2006

Abstract — Quantum chemical calculations of neutral and charged (H₂O)_n water clusters modeling fragments of a real hydrogen-bond network of water and dynamic simulations of the clusters either upon the electron removal from a stable neutral cluster or upon the excitation of various cluster vibrations enabled us to distinguish separate stages of the structure reorganization. Thermal motion of molecules in a liquid modeled by the low-frequency rotational vibrations and swinging of molecules prevents the formation of cations with the opti-mum mutual arrangement of the OH radical and H₃O⁺ ion. Judging from the typical periods of reactive vibra-tions and those motions, which impede the desired structure reorganization, the most probable should be the formation of OHH₂OH₃O⁺ fragments in liquid water. The energy necessary for the ionization of superficial water layers (at the irradiation) can be estimated from the intermediate ionization potentials of water clusters. Extrapolating the dependence of these potentials on the number of water molecules constituting the cluster provided the first ever theoretical estimate of the threshold ionization energy of water: 9.5 eV.

PACS numbers: 31.15.Ar; 31.15.Qg; 33.15.Ry; 34.50.Ez; 36.40.Wa