Quantum tunnelling plays a major role in muonium reactions with larger alkanes
01 Sep 2021



Scientists have found that quantum tunnelling has a dramatic effect on the rate of reaction that occurs when muonium reacts with larger alkanes.

Don Fleming and Abdel Jawad on the EMU instrument.

​​​​Don Fleming and Abdel Jawad on the EMU instrument.​


​Muonium (Mu = μ+ e− ), formed spontaneously when muons are stopped in many materials, acts as the lightest isotope of hydrogen. By measuring the kinetics of its reactions, and comparing with other hydrogen isotopes, scientists are able to quantify its kinetic isotope effects (KIEs). This study, published in PCCP, focuses on the abstraction of a hydrogen atom from propane and n-butane by muonium, compared to similar reactions of the hydrogen atom. 

Unlike previous experiments on the lighter alkanes, methane and ethane, their results showed that quantum tunnelling plays a much more major role than expected. Through their uniquely important experiments, these researchers showed that tunnelling had a dramatic effect on the reaction rates. 

The outcome of this study posed a considerable challenge to accepted reaction rate theory on hydrogen-atom reactions in alkane systems. Recent work by Gao et. al. has partially addressed this challenge, but discrepancies between quantum theory and experiment still remain. In the future, these researchers plan on using additional techniques to fully probe both the degree and effects of this tunnelling behaviour.

Related publications: “Rate constants and kinetic isotope effects for H-atom abstraction reactions by muonium in the Mu + propane and Mu + n-butane reactions from 300 K to 435 K: challenges for theory.” Phys. Chem. Chem. Phys., 22, 6326-6334 (2020) 

DOI: 10.1039/C9CP06822H​

Contact: Jones, Evan (STFC,RAL,ISIS)