Kinetics and mechanism of water cluster equilibria.

We combine hybrid density functional and transition state theory to investigate dynamical and mechanistic features of important aggregation, isomerization, and exchange pathways for cluster constituents of liquid water, building on the general concepts of quantum cluster equilibrium (QCE) theory. Such calculations confirm the extreme dynamical volatility of leading water cluster structural motifs, consistent with known ultrafast relaxation properties of liquid water and contrary to the superficial static imagery often associated with thermodynamic-level description. We identify low-barrier mechanistic pathways and associated donor-acceptor orbital interactions that lead to facile scrambling of covalent and H-bond cluster motifs with remarkably small energetic barriers, significantly less than required to break even a single covalent or H-bond in isolation.