Short H-bonds and spontaneous self-dissociation in „H2O...20: Effects of H-bond topology

There are 30026 symmetry-distinct ways to arrange 20 water molecules in a dodecahedral cage with nearly optimum hydrogen bond lengths and angles, analogous to the arrangements that give rise to the zero-point entropy in ice-Ih. The energy of hydrogen bond isomers in (H2O)20 , assumed to be similar in the past, differs by up to 70 kcal/mol. The isomers differ widely in their hydrogen bond lengths, some exhibiting bond lengths as short as ;2.4 Å. The differences among the isomers extends to their chemical properties: In some arrangements one or more water molecules spontaneously self-dissociate, giving rise to spatially separated excess proton and hydroxyl ion units in the cluster. Isomers that exhibit these unusual properties can be identified by features of their hydrogen bond topology. © 2003 American Institute of Physics. @DOI: 10.1063/1.1538240#