Term: tunnelling
https://doi.org/10.1351/goldbook.T06531

Definition:
The process by which a particle or a set of particles crosses a barrier on its potential-energy (reaction) surface without having the energy required to surmount this barrier. Since the rate of tunnelling decreases with increasing reduced mass, it is significant in the context of isotope effects of hydrogen isotopes.

Related Terms:
1) potential-energy (reaction) surface (http://doi.org/10.1351/goldbook.P04780).
2) reduced mass (http://doi.org/10.1351/goldbook.R05214).
3) isotopes (http://doi.org/10.1351/goldbook.I03331).

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1174 (https://doi.org/10.1351/pac199466051077)

Citation: 'tunnelling' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.T06531

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