第111回計算科学コロキウムを、10月14日（金）に開催します。
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日時：2016年10月14日（金） 10:30-12:00
場所：筑波大学　計算科学研究センター　　会議室C
題目：Instanton Theory and the Role of Atom-Tunneling in Astrochemical Reactions
講師：Prof. Dr. Johannes Kästner
University of Stuttgart Inst. for Theoretical Chemistry

要旨:
Simulations of reaction rates including quantum tunneling of atoms complement measurements provide input for astrochemical models. An appropriate rate theory must be accurate enough to provide reliable predictions, but efficient enough to allow for computationally intensive electronic structure calculations at large enough structural models. Instanton theory, based on Feynman path integrals, matches these requirements [1]. It provides the dominant tunneling path at a given temperature or energy.
We have used instanton theory to calculate rate constants for a number of reactions of astrochemical interest both in the gas phase and on surfaces. Examples are:
H₂ + OH ⟶ H₂O + H [2]
CH₃OH + H˙⟶˙CH₂OH + H₂ [3]
HNCO + H ⟶ NH₂CO [4]
Models of surface reactions need to include the interplay between reactions and diffusion.

Figure 1: Tunneling path (instanton path) of the reaction HNCO + H ⟶ NH2CO on a surface of amorphous solid water [4]. The path is colored from the reactant side (red) to the product side (blue).

References
[1] J. Meisner and J. Kästner, 2016, Angew. Chem. Int. Ed. 55, 5400
[2] J. Meisner and J. Kästner, 2016, J. Chem. Phys. 144, 174303
[3] T.P.M. Goumans, J. Kästner, 2011, J. Phys. Chem. A 115, 10767
[4] L. Song and J. Kästner, 2016, Phys. Chem. Chem. Phys. accepted

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