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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 3 - TUNNELCHEM (Atom-Tunneling in Chemistry)

Teaser

Summary

Atom tunneling is a quantum phenomenon which accelerates chemical reactions. We investigate its effect on chemical reactions is very diverse areas of chemistry. We have found significant tunneling effects in astrochemistry and work on its investigation in biochemical processes. Because of its quantum nature, atom tunneling is difficult to treat computationally. We develop methods to calculate the tunneling probability more efficiently and more accurately than previously possible.

Work performed

We investigated the phenomenon of atom tunneling in chemical reactions using several approaches. We developed method to simulate tunneling rate constants with higher accuracy and lower computational demand than previously possible. This was achieved by deriving a microcanonic formulation of instanton theory along with an extension of instanton theory to higher temperatures. This allows the calculation of bimolecular rate constants over the whole temperature range over a large range of pressures. The computational efficiency was increased by a dual-level scheme for instanton theory, as well as by employing machine-learning techniques for the approximation of potential energy surfaces.
We applied it to many reactions relevant to the interstellar medium, gas phase reactions as well as surface reactions. The resulting rate constants were subsequently used in astrochemical models and resulted in improved agreement with observed abundancies. The tunnel effect is also important in biochemical systems (enzymes). We investigated the enzyme Taurine/alpha-ketoglutarate Dioxygenase (TauD). Moreover, we have written a review paper on atom tunneling in chemistry and currently edit a textbook on the same subject.

Final results

Our tunneling rate constants for astrochemical reactions will significantly increase our understanding of interstellar chemical processes. To achieve that, microcanonical tunneling rates are necessary. We now have developed an algorithm to calculate these accurately and efficiently.