Kinetics of the reaction of the heaviest hydrogen atom with H2, the 4Heμ + H24HeμH + H reaction

Experiments, accurate quantal calculations, and variational transition state theory, including kinetic isotope effects for a factor of 36.1 in isotopic mass

Donald G. Fleming, Donald J. Arseneau, Oleksandr Sukhorukov, Jess H. Brewer, Steven L. Mielke, Donald G. Truhlar, George C. Schatz, Bruce C. Garrett, Kirk A. Peterson

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

The neutral muonic helium atom 4Heμ, in which one of the electrons of He is replaced by a negative muon, may be effectively regarded as the heaviest isotope of the hydrogen atom, with a mass of 4.115 amu. We report details of the first muon spin rotation (μSR) measurements of the chemical reaction rate constant of 4Heμ with molecular hydrogen, 4Heμ + H24HeμH + H, at temperatures of 295.5, 405, and 500 K, as well as a μSR measurement of the hyperfine coupling constant of muonic He at high pressures. The experimental rate constants, kHeμ, are compared with the predictions of accurate quantum mechanical (QM) dynamics calculations carried out on a well converged Born-Huang (BH) potential energy surface, based on complete configuration interaction calculations and including a Born-Oppenheimer diagonal correction. At the two highest measured temperatures the agreement between the quantum theory and experiment is good to excellent, well within experimental uncertainties that include an estimate of possible systematic error, but at 295.5 K the quantum calculations for kHeμ are below the experimental value by 2.1 times the experimental uncertainty estimates. Possible reasons for this discrepancy are discussed. Variational transition state theory calculations with multidimensional tunneling have also been carried out for kHeμ on the BH surface, and they agree with the accurate QM rate constants to within 30% over a wider temperature range of 200-1000 K. Comparisons between theory and experiment are also presented for the rate constants for both the D + H2 and Mu + H2 reactions in a novel study of kinetic isotope effects for the H + H2 reactions over a factor of 36.1 in isotopic mass of the atomic reactant.

Original languageEnglish
Article number184310
JournalJournal of Chemical Physics
Volume135
Issue number18
DOIs
Publication statusPublished - Nov 14 2011

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Kinetic theory
kinetic theory
Isotopes
isotope effect
Hydrogen
Rate constants
hydrogen atoms
Atoms
Kinetics
kinetics
Experiments
Helium
Potential energy surfaces
Quantum theory
Systematic errors
muon spin rotation
Temperature
Reaction rates
Chemical reactions
helium atoms

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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Kinetics of the reaction of the heaviest hydrogen atom with H2, the 4Heμ + H24HeμH + H reaction : Experiments, accurate quantal calculations, and variational transition state theory, including kinetic isotope effects for a factor of 36.1 in isotopic mass. / Fleming, Donald G.; Arseneau, Donald J.; Sukhorukov, Oleksandr; Brewer, Jess H.; Mielke, Steven L.; Truhlar, Donald G.; Schatz, George C.; Garrett, Bruce C.; Peterson, Kirk A.

In: Journal of Chemical Physics, Vol. 135, No. 18, 184310, 14.11.2011.

Research output: Contribution to journalArticle

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abstract = "The neutral muonic helium atom 4Heμ, in which one of the electrons of He is replaced by a negative muon, may be effectively regarded as the heaviest isotope of the hydrogen atom, with a mass of 4.115 amu. We report details of the first muon spin rotation (μSR) measurements of the chemical reaction rate constant of 4Heμ with molecular hydrogen, 4Heμ + H2 → 4HeμH + H, at temperatures of 295.5, 405, and 500 K, as well as a μSR measurement of the hyperfine coupling constant of muonic He at high pressures. The experimental rate constants, kHeμ, are compared with the predictions of accurate quantum mechanical (QM) dynamics calculations carried out on a well converged Born-Huang (BH) potential energy surface, based on complete configuration interaction calculations and including a Born-Oppenheimer diagonal correction. At the two highest measured temperatures the agreement between the quantum theory and experiment is good to excellent, well within experimental uncertainties that include an estimate of possible systematic error, but at 295.5 K the quantum calculations for kHeμ are below the experimental value by 2.1 times the experimental uncertainty estimates. Possible reasons for this discrepancy are discussed. Variational transition state theory calculations with multidimensional tunneling have also been carried out for kHeμ on the BH surface, and they agree with the accurate QM rate constants to within 30{\%} over a wider temperature range of 200-1000 K. Comparisons between theory and experiment are also presented for the rate constants for both the D + H2 and Mu + H2 reactions in a novel study of kinetic isotope effects for the H + H2 reactions over a factor of 36.1 in isotopic mass of the atomic reactant.",
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T2 - Experiments, accurate quantal calculations, and variational transition state theory, including kinetic isotope effects for a factor of 36.1 in isotopic mass

AU - Fleming, Donald G.

AU - Arseneau, Donald J.

AU - Sukhorukov, Oleksandr

AU - Brewer, Jess H.

AU - Mielke, Steven L.

AU - Truhlar, Donald G.

AU - Schatz, George C.

AU - Garrett, Bruce C.

AU - Peterson, Kirk A.

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AB - The neutral muonic helium atom 4Heμ, in which one of the electrons of He is replaced by a negative muon, may be effectively regarded as the heaviest isotope of the hydrogen atom, with a mass of 4.115 amu. We report details of the first muon spin rotation (μSR) measurements of the chemical reaction rate constant of 4Heμ with molecular hydrogen, 4Heμ + H2 → 4HeμH + H, at temperatures of 295.5, 405, and 500 K, as well as a μSR measurement of the hyperfine coupling constant of muonic He at high pressures. The experimental rate constants, kHeμ, are compared with the predictions of accurate quantum mechanical (QM) dynamics calculations carried out on a well converged Born-Huang (BH) potential energy surface, based on complete configuration interaction calculations and including a Born-Oppenheimer diagonal correction. At the two highest measured temperatures the agreement between the quantum theory and experiment is good to excellent, well within experimental uncertainties that include an estimate of possible systematic error, but at 295.5 K the quantum calculations for kHeμ are below the experimental value by 2.1 times the experimental uncertainty estimates. Possible reasons for this discrepancy are discussed. Variational transition state theory calculations with multidimensional tunneling have also been carried out for kHeμ on the BH surface, and they agree with the accurate QM rate constants to within 30% over a wider temperature range of 200-1000 K. Comparisons between theory and experiment are also presented for the rate constants for both the D + H2 and Mu + H2 reactions in a novel study of kinetic isotope effects for the H + H2 reactions over a factor of 36.1 in isotopic mass of the atomic reactant.

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