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Updated: Apr 11, 2026
05:51
Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method
Published on: July 19, 2019
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Quantum tunneling observed without its characteristic large kinetic isotope effects
Tetsuya Hama1, Hirokazu Ueta2, Akira Kouchi2
1Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan hama@lowtem.hokudai.ac.jp.
Summary
Cold atoms tunnel during reactions on solid benzene, but show small kinetic isotope effects. This suggests surface diffusion controls reaction rates, potentially impacting interstellar chemistry and deuterium enrichment.
Area of Science:
- Physical Chemistry
- Surface Science
- Astrochemistry
Background:
- Quantum tunneling is crucial for chemical kinetics, often indicated by kinetic isotope effects (KIEs).
- Anomalously large reaction efficiencies in some systems suggest quantum tunneling plays a significant role.
Purpose of the Study:
- To experimentally investigate quantum tunneling of hydrogen and deuterium atoms on solid benzene.
- To determine the influence of surface diffusion on the observed kinetic isotope effect.
Main Methods:
- Experimental study of cold hydrogen (H) and deuterium (D) atom addition to solid benzene.
- Measurement of the H/D kinetic isotope effect (KIE) for the surface reaction.
Main Results:
- Cold H and D atoms add to solid benzene via tunneling.
- Observed H/D KIE was small (1-1.5), significantly lower than the intrinsic tunneling KIE (≳ 100).
- Surface diffusion of H/D atoms, not tunneling, controlled the reaction kinetics.
Conclusions:
- Quantum tunneling in surface and interfacial systems may not always exhibit large KIEs and could be overlooked.
- Surface tunneling reactions on interstellar dust may contribute to deuteration of hydrocarbons.
- Findings offer insights into interstellar physicochemical processes and deuterium enrichment in meteorites.
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