Now we're talking! Odd as it seems, this reaction provides crucial clues to reaction dynamics in which both dipole and lone pair interactions have a role. It does not turn out to be atmospherically significant, but that is actually not as obvious as you might think. Look for Dubey et al in there near future to find out more.
A schematic of the symmetric minimum energy path of the HO + HOH . HOH + OH reaction is shown. The surface depicts the global minimum (of the many local minima) for the OH-OH2 complex as well as the transition state to proton transfer. The transition state may be higher (solid line) or lower (dash line) in energy than the reagents, depending on the extent that the long range forces stabililizing the complex are preserved and augmented by short range interactions. We expect slow proton exchange for the high barrier while fast proton transfer for the barrierless case. Optimized configurations (UHF/6-31G**) of the reactants, complex, and transition state are shown on the left side of the transition state. The evolution of electrostatic and orbital interactions as the reagents transform to the complex and then the transition sate are presented on the right. Dark and light shades indicate the phase of the molecular orbitals. Dipoles are indicated by d+ and d- on the reactants and complex. The complex is stabilized by dipolar attractions and bonding interactions from delocalizing the lone pair on O in the HOH molecule towards OH. The transition state is stabilized by the net interaction of the SOMO of the HO radical with an inner shell H-O s bonding orbital in HOH. We measure the proton transfer rate by isotopically labeling either an oxygen atom (as shown in the figure with different shades of blue) or a terminal hydrogen. In this work we demonstrate that this reaction is slow (high barrier) and show that a complex interplay of dipolar, frontier-, and reactive- orbital interactions governs the reaction path.