Spectroscopic characterization of the five possible orientations of a hydrogen-bonded pair of water molecules within the cubic water octamer framework

Among the 14 conformers of the cubic water octamer, there are 114 symmetry-unique pairs of nearest-neighbor water molecules. The pairs can be divided into 5 classes based on hydrogen bonding topology. These 5 possible relative orientations are studied via isotopic replacement. Individual calculations were carried out by systematically replacing selected subsets of the 16 hydrogen atoms of a given (H2O)8 conformer with deuterium atoms and then performing second-order Moeller-Plesset perturbation theory calculations of the clusters. From this analysis, it was found that, for a given orientation, the vibrational frequencies of the covalent O··H bonds for the 5 nearest-neighbor water pairs fall into distinct ranges. This information can be used to spectroscopically identify the different water structures by their unique water topologies and unique spectral signature