Rate constants from instanton theory via a microcanonical approach

Abstract

Microcanonical instanton theory offers the promise of providing rate constants for chemical reactions including quantum tunneling of atoms over the whole temperature range. We discuss different rate expressions, which require the calculation of stability parameters of the instantons. The traditional way of obtaining these stability parameters is shown to be numerically unstable in practical applications. We provide three alternative algorithms to obtain such stability parameters for non-separable systems, i.e., systems in which the vibrational modes perpendicular to the instanton path couple to movement along the path. We show the applicability of our algorithms on two molecular systems: H${}_2$ + OH $\to$ H${}_2$O + H using a fitted potential energy surface and HNCO + H $\to$ NH${}_2$CO using a potential obtained on-the-fly from density functional calculations.

References in corpus (3)

• Atom-Tunneling in Chemistry
• Formation of the prebiotic molecule NH${}_2$CHO on astronomical amorphous solid water surfaces: accurate tunneling rate calculations
• Quantum tunneling during interstellar surface-catalyzed formation of water: the reaction H + H${}_2$O${}_2$ $\to$ H${}_2$O + OH

Cited by in corpus (9)

• Atom Tunneling in the Water Formation Reaction H${}_2$ + OH $\to$ H${}_2$O + H on an Ice Surface
• Tunneling Reaction Kinetics for the Hydrogen Abstraction Reaction H + H${}_2$S -> H${}_2$ + HS in the Interstellar Medium
• Instanton Rate Constant Calculations Close to and Above the Crossover Temperature
• Dual-Level Approach to Instanton Theory
• Potential energy surface interpolation with neural networks for instanton rate calculations
• Low-Temperature Kinetic Isotope Effects in CH3OH+H -> CH2OH+H2 Shed Light on the Deuteration of Methanol in Space
• Comparison of classical reaction paths and tunneling paths studied with the semiclassical instanton theory
• Calculation of Reaction Rate Constants in the Canonical and Microcanonical Ensemble
• Divide-and-Conquer Method for Instanton Rate Theory