New Insights into the Dynamics of Concerted Proton Tunneling in Cyclic Water and Hydrogen Fluoride Clusters

Abstract

The concerted proton transfer hypersurface of cyclic water and hydrogen fluoride clusters has been described by high-level molecular quantum mechanical calculations. For the cyclic water clusters the concerted proton transfer transition states have been investigated for the first time with methods including treatment of dynamic electron correlation. The crucial importance of dynamic electron correlation for the barrier heights is demonstrated. A detailed analysis of the minimum energy path has been performed. The reaction swath of the concerted proton transfer was examined indicating a reasonable description by harmonic approximation of the energy hypersurface. Transfer rates have been calculated by means of variational transition state theory with interpolated corrections (VTST-IC) and dual-level direct dynamics (DLDD), both with semiclassical tunneling corrections. Tunneling is very efficient in the concerted proton exchange reaction of the cyclic hydrogen-bonded clusters under investigation. Rate const...