PNNL

Abstract

We report the first harmonic vibrational spectra for each of the lowest lying isomers within the four major families of minima of (H2O)20, namely the dodecahedron, fused cubes, face-sharing pentagonal prisms and edge-sharing pentagonal prisms. These were obtained at the second-order Møller-Plesset perturbation level of theory (MP2) with the augmented correlation consistent basis set of double zeta quality (aug-cc-pVDZ) at the corresponding minimum energy geometries. The computed infrared (IR) spectra are the first ones obtained from first principles for these clusters. They were found to contain spectral features, which can be directly mapped onto the distinctive spectroscopic signatures of their constituent tetramer, pentamer and octamer fragments. The dodecahedron spectra show the richest structure in the OH stretching region and are associated with the most red-shifted OH vibrations with respect to the monomer. The lowest lying face-sharing pentagonal prism isomer displays intense IR active vibrations that are red-shifted by ~600 cm-1 with respect to the water monomer. The zero-point energy corrected MP2/CBS (complete basis set) limit binding energies (D0) for the four isomers are –163.1 kcal/mol (face-sharing pentagonal prism), -160.1 kcal/mol (edgesharing pentagonal prism), -157.5 kcal/mol (fused cubes) and –148.1 kcal/mol (dodecahedron).