Kinetic Isotope Effects for the Reactions of Muonic Helium and Muonium with H

The neutral muonic helium atom may be regarded as the heaviest isotope of the hydrogen atom, with a mass of approximately 4.1 atomic mass units (⁴.¹H), because the negative muon almost perfectly screens one proton charge. We report the reaction rate of ⁴.¹H with ¹H₂ to produce ⁴.¹H¹H + ¹H at 295 to...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 2011-01, Vol.331 (6016), p.448-450
Main Authors: Fleming, Donald G, Arseneau, Donald J, Sukhorukov, Oleksandr, Brewer, Jess H, Mielke, Steven L, Schatz, George C, Garrett, Bruce C, Peterson, Kirk A, Truhlar, Donald G
Format: Article
Language:English
Subjects:
Approximation
Atomic mass
Atoms
Electrons
Isotopes
Kinetic isotope effect
Muonium
Muons
Physical chemistry
Quantum tunneling
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Summary:The neutral muonic helium atom may be regarded as the heaviest isotope of the hydrogen atom, with a mass of approximately 4.1 atomic mass units (⁴.¹H), because the negative muon almost perfectly screens one proton charge. We report the reaction rate of ⁴.¹H with ¹H₂ to produce ⁴.¹H¹H + ¹H at 295 to 500 kelvin. The experimental rate constants are compared with the predictions of accurate quantum-mechanical dynamics calculations carried out on an accurate Born-Huang potential energy surface and with previously measured rate constants of ⁰.¹¹H (where ⁰.¹¹H is shorthand for muonium). Kinetic isotope effects can be compared for the unprecedentedly large mass ratio of 36. The agreement with accurate quantum dynamics is quantitative at 500 kelvin, and variational transition-state theory is used to interpret the extremely low (large inverse) kinetic isotope effects in the 10⁻⁴ to 10⁻² range.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.1199421