Molecular model of dielectric relaxation and the far-infrared isotopic effect in liquid H2O and D2O

The wideband (dielectric + far-infrared(1)) spectra of liquid H2O and D2O are described in terms of two potential wells, to which two types of molecular motion correspond with different values of a dipole moment. One well is narrow and steep with a flat bottom, flat brim and rectangular shape. Another well is concave and has a cosine squared (CS) shape. The steep rectangular (hat-like) well determines reorientation of dipoles; the concave well determines motions specific for the H-bonded water molecules. This type of motion, being connected to the far-infrared (FIR) translational band (near 200 cm(-1)), is more chaotic than reorientation, which is responsible for the intense librational band in the region 500 - 800 cm-1. The lifetime of the CS well is shorter than that of the hat well. Few mechanisms contributing to the dielectric/FIR spectra of liquid water are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.