Research & Teaching Faculty

Zero-point energy, tunnelling, and vibrational adiabaticity in the Mu + H-2 reaction

TitleZero-point energy, tunnelling, and vibrational adiabaticity in the Mu + H-2 reaction
Publication TypeJournal Article
Year of Publication2015
AuthorsMielke, SL, Garrett, BC, Fleming, DG, Truhlar, DG
Date PublishedJAN 17

Isotopic substitution of muonium for hydrogen provides an unparalleled opportunity to deepen our understanding of quantum mass effects on chemical reactions. A recent topical review in this journal of the thermal and vibrationally state-selected reaction of Mu with H-2 raises a number of issues that are addressed here. We show that some earlier quantum mechanical calculations of the Mu + H-2 reaction, which are highlighted in this review, and which have been used to benchmark approximate methods, are in error by as much as 19% in the low-temperature limit. We demonstrate that an approximate treatment of the Born-Oppenheimer diagonal correction that was used in some recent studies is not valid for treating the vibrationally state-selected reaction. We also discuss why vibrationally adiabatic potentials that neglect bend zero-point energy are not a useful analytical tool for understanding reaction rates, and why vibrationally non-adiabatic transitions cannot be understood by considering tunnelling through vibrationally adiabatic potentials. Finally, we present calculations on a hierarchical family of potential energy surfaces to assess the sensitivity of rate constants to the quality of the potential surface.