Large curvature tunnelling on the reaction path

Area of Science:

• Quantum Chemistry
• Chemical Dynamics
• Computational Chemistry

Background:

• The reaction path Hamiltonian is a theoretical framework used in chemical dynamics.
• Its application to hydrogen tunnelling dynamics, especially with large path curvature, has been limited.
• This limitation is particularly relevant for hydrogen exchange reactions.

Purpose of the Study:

• To identify fundamental limitations of the reaction path formulation for hydrogen tunnelling.
• To propose a novel computational approach for accurately treating hydrogen tunnelling dynamics.
• To overcome the challenges posed by large path curvature in chemical reactions.

Main Methods:

• A two-dimensional model simulating intramolecular hydrogen transfer in malonaldehyde was used.
• The study critically evaluated commonly used approximations within the reaction path formulation.
• A new non-orthogonal Hamiltonian representation using distributed local harmonic oscillators was developed.

Main Results:

• Common approximations in the reaction path formulation can yield misleading results for hydrogen tunnelling.
• The proposed distributed harmonic oscillator approach provides an exact variational limit for any reaction path curvature.
• This new method demonstrates stability against reaction path variations and can handle bifurcating paths.

Conclusions:

• The standard reaction path Hamiltonian has inherent limitations for complex hydrogen tunnelling dynamics.
• The novel distributed harmonic oscillator method offers a more robust and accurate treatment of hydrogen tunnelling.
• This approach enhances the ability to model complex chemical reactions involving hydrogen transfer.