Muonium (Mu = μ+
), 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)