Reorientation of water molecules in solid hydrates. Correlation with spectroscopic and structural data

Abstract

A review is presented of experimentally known activation energies, E_a, for the 180° flip motion of the H₂O molecule about its two-fold axis in 30 different solid hydrates. The relationship between E_a and other parameters characterizing a hydrogen bond is discussed. Diagrams correlating E_a with the hydrogen-bond length, R_O⋯X, stretching frequency, ν_OH, librational twist frequency, ν_tw, and deuterium quadrupole coupling constant, e²qQ/h, are presented. The dependence of these correlations on the coordination of the water molecule is discussed, and it is clear that the number of atoms coordinating the water molecule is one of the main factors determining the flip activation energy E_a. The activation energy and the librational twist frequency display a strong correlation, with an associated correlation coefficient of 0.90.