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

E-mail: juliet@classic.chem.msu.su

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 distin-
guish 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 pro-
vided 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

DOI: 10.1134/S0033173207010031

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