Distribution of topologically distinct isomers of water clusters and dipole moments of constituent water molecules at finite atmospheric temperatures.

Abstract

Hydrogen-bonding (HB) patterns correspond to topologically distinct isomers of a water cluster and can be expressed by digraphs. We make use of the HB pattern to divide the configuration space of a water cluster ((H2O)n, n = 3-8) at a finite temperature. Each configuration of a water cluster generated in Monte Carlo (MC) simulation is classified into an HB pattern. The number of observed HB patterns increases exponentially with the cluster size, whereas the population of the most abundant HB pattern decreases. The populations of the HB patterns are transformed into the relative Helmholtz energies. At a finite temperature, it can be observed that isomers other than local minimum structures on the potential energy surface are highly populated. The dipole moment of a constituent molecule in a water cluster is enhanced, depending on the molecular circumstance. The change is rationalized by the difference in the local HB type of the water molecule in the HB network.