The C6H6–(H2O)2 complex: Theoretical predictions of the structure, energetics, and tunneling dynamics

A detailed theoretical study of the C6H6–(H2O)2 complex is presented. We characterize the structure and energy by means of various potentials and correlated ab initio calculations. The potential surface is extremely flat but the structures obtained with the empirical potentials and ab initio optimizations agree fairly well. Transition states and corresponding reaction paths are calculated for four possible degenerate rearrangements. The splittings for these mechanisms are calculated from quantum simulations with the diffusion Monte Carlo (DMC) approach. We predict that two splittings should be observable in the spectrum. The DMC calculations also allow prediction of vibrationally averaged structures, bond energies, and rotational constants.