Kinetic Isotope Effects for the Reactions of Muonic Helium and Muonium with H2

  title={Kinetic Isotope Effects for the Reactions of Muonic Helium and Muonium with H2},
  author={Donald G. Fleming and Donald J Arseneau and Oleksandr Sukhorukov and Jess H. Brewer and Steven L. Mielke and George C. Schatz and Bruce C. Garrett and Kirk A. Peterson and Donald G. Truhlar},
  pages={448 - 450}
Calculated reaction rates for two hydrogen isotopes, one 36 times heavier than the other, agree with experiments at 500 kelvin. The neutral muonic helium atom may be regarded as the heaviest isotope of the hydrogen atom, with a mass of ~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… 
Understanding the reaction between muonium atoms and hydrogen molecules: zero point energy, tunnelling, and vibrational adiabaticity
The advent of very precise measurements of rate coefficients in reactions of muonium (Mu), the lightest hydrogen isotope, with H2 in its ground and first vibrational state and of kinetic isotope
Dynamics of the reactions of muonium and deuterium atoms with vibrationally excited hydrogen molecules: tunneling and vibrational adiabaticity.
Quantum mechanical and quasiclassical trajectory calculations have been carried out for the exchange reactions of D and Mu with hydrogen molecules in their ground and first vibrational states, finding that at the lowest possible energies, the non-adiabatic vibrational crossing implies a strong tunneling effect through the ν = 1 adiabatic barrier.
Rate constants for the slow Mu + propane abstraction reaction at 300 K by diamagnetic RF resonance.
The measured rate constant, kMu, is surprisingly only about a factor of three slower than that expected for H + C3H8, indicating a dominant contribution from quantum tunneling in the Mu reaction, consistent with elementary transition state theory calculations of the kMu/kH kinetic isotope effect.
Muonium Addition Reactions and Kinetic Isotope Effects in the Gas Phase: k∞ Rate Constants for Mu + C2H2.
Comparisons with data and with calculations for the corresponding H(D) + C2H2 addition reactions reveal a much faster rate for the Mu reaction at the lowest temperatures, by 2 orders of magnitude, in accord with the propensity of Mu to undergo quantum tunneling.
Negative muon chemistry: the quantum muon effect and the finite nuclear mass effect.
This study reveals that the differences in the ionization potentials of isoelectronic muonic atoms and regular atoms are of the order of millielectronvolts and that for the valence ionizations of muonic helium and muonic lithium the nuclear mass effects are more important.
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.
Measurements of the temperature dependence of the rate constants for H-atom abstraction reactions from propane and n-butane by the light isotopic H- atom muonium (Mu), kMu(T), over temperatures in the range 300 K to 435 K yield activation energies, EMua, that are much lower than estimated from zero-point-energy corrected vibrationally adiabatic potential barriers.
Can quasiclassical trajectory calculations reproduce the extreme kinetic isotope effect observed in the muonic isotopologues of the H + H2 reaction?
The analysis of the results shows that the large zero point energy of the MuH product is the key factor for the large KIE observed.
New Perspectives in Muonium Chemical Reactions
One can produce two "isotopes" of the H atom utilizing positive or negative muons, "muonium (0.114 amu) and "muonic helium (4.11 amu)." These isotopes can be used to probe large isotope effects with
Zero-point energy, tunnelling, and vibrational adiabaticity in the Mu + H2 reaction
Isotopic substitution of muonium for hydrogen provides an unparalleled opportunity to deepen our understanding of quantum mass effects on chemical reactions. A recent topical review in this journal


Theoretical rate constants and kinetic isotope effects in the reaction of methane with H, D, T, and Mu atoms.
In the comparison of the reactivity between protium and muonium, which is the most severe test of the surface and theoretical method due to the large mass difference between the two isotopes, some sources of discrepancy between theory and experiment were analyzed.
Muonium. A light isotope of hydrogen
Muonium differs from hydrogen only by virtue of having the light, short-lived positive muon as its nucleus rather than a proton. This review of the chemistry of muonium emphasises its role as a
Experimental tests of reaction rate theory: Mu+H2 and Mu+D2
Bimolecular rate constants for the thermal chemical reactions of muonium (Mu) with hydrogen and deuterium—Mu+H2→MuH+H and Mu+D2→MuD+D—over the temperature range 473–843 K are reported. The Arrhenius
Formation of the muonic helium atom
A full description is given of an experiment in which the muonic helium atom, /sup 4/ -/e/sup -/, was first observed. The method of the experiment was to study the precession of the
Dynamics of gas-phase reactions of muonium
Applications of variational transition state theory with semiclassical adiabatic transmission coefficients to the reactions of muonium with H2, D2, F2, and Cl2 are reviewed. In addition new
H+H2 thermal reaction: a convergence of theory and experiment.
Experimental and theory now agree perfectly, within experimental error, bringing this 75-year-old scientific problem to completion, H+H2-->H2+H.
Ab Initio Predictions and Experimental Confirmation of Large Tunneling Contributions to Rate Constants and Kinetic Isotope Effects for Hydrogen Atom Transfer Reactions
in DME was added by syringe pump over 24 h to a refluxing suspension of McMurry Ti reagent from Zn-Cu and TiC13 in DME.14 After a further 18 h at reflux, neutral workup and chromatography over Si
Coupling of hydrogenic tunneling to active-site motion in the hydrogen radical transfer catalyzed by a coenzyme B12-dependent mutase
These calculations confirm that tunneling contributions can be large enough to explain even a kinetic isotope effect >50, not because the barrier is unusually thin but because corner-cutting tunneling decreases the distance over which the system tunnels without a comparable increase in either the effective potential barrier or the effective mass for tunneling.