Collect. Czech. Chem. Commun. 1980, 45, 3417-3435

Isomerism, energetics, and thermodynamics of (H2O)2 and its role in real gas phase of water

Zdeněk Slanina

The J. Heyrovský Institute of Physical Chemistry and Electrochemistry, Czechoslovak Academy of Sciences, 121 38 Prague 2


Recent ab initio SCF CI potential energy hypersurfaces of (H2O)2 have been systematically investigated with the use of an automatic optimization procedure working with analytically constructed energy gradient with the aim to localize all their stationary points lying in the relevant region. For these stationary points the vibrational analysis has been carried out based on analytically constructed second derivatives of energy with correct respecting of the eight redundancy conditions introduced into the problem by the original choice of the coordinates. Out of the six localized stationary points only one has been found to be a minimum, three of them represent transition states, and the remaining two are higher types of stationary points. Relation of the analytically and the numerically constructed force constant matrices and possibility of the occurrence of extraneous stationary points have been studied. The calculated harmonic vibrational frequencies corresponding to the energy minimum show reasonable agreement with available experimental data. On the basis of the generated molecular parameters of the minimum the thermodynamics of formation of the water dimer has been described within a broad temperature interval, and a good agreement with experimental findings has been obtained. Role of the water dimer in real gas phase of water has been analyzed, and contribution of (H2O)2 to value of the second virial coefficient of water vapour has been evaluated. Within the framework of the given quantum-chemical methodological level, this study has led to negation of possibility of isomerism of (H2O)2 with respect to equilibrium problems, it has, however, shown the isomerism in the case of kinetics of interconversion of (H2O)2.