Hydrogen bonding in cubic (H2O)8 and OH∙(H2O)7 clusters

Abstract

A systematic study is presented for $\mathrm{OH}\bullet {\left({\mathrm{H}}_2\mathrm{O}\right)}_7$ clusters derived from the cubic ${\left({\mathrm{H}}_2\mathrm{O}\right)}_8$ octamer by replacing one water with a hydroxyl radical. The system is a prototype for atmospheric water clusters containing the environmentally important OH species, and for OH adsorbed at the surface of ice. The full set of 39 symmetry-distinct cubic $\mathrm{OH}\bullet {\left({\mathrm{H}}_2\mathrm{O}\right)}_7$ clusters is enumerated, and the structures are determined using ab initio quantum chemical methods. Graph invariants are employed to obtain a unified analysis of the stability and structure of cubic ${\left({\mathrm{H}}_2\mathrm{O}\right)}_8$ and $\mathrm{OH}\bullet {\left({\mathrm{H}}_2\mathrm{O}\right)}_7$, relating these physical properties to the various hydrogen-bond topologies present in these clusters. To accomplish this the graph invariant formalism is extended to treat a hydrogen bonding impurity within a pure water network.