Epithermal muonium processes in methane and propane gases

Kempton, J. R.; Arseneau, Donald J.; Fleming, Donald G.; Senba, M.; Gonzalez, Alicia C.; Pan, Jingwen; Tempelmann, A.; Garner, David M.

doi:10.1021/j100172a043

Cited by 10 publications

(12 citation statements)

References 11 publications

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“…The full Mu amplitude, A Mu = 0.14 AE 0.04, accounting for the unobserved singlet fraction, suggests that the fraction of Mu formed, f Mu , is B60%, which is low compared to previous reports of absolute polarizations where this fraction was found to be closer to 70% at a comparable propane pressure. 35 Our TF measurements of the Dia amplitude do not separate contributions due to muon stops in the target walls from the fraction formed in the gas, the latter due to muon molecular ions 37,41 as well as to ''hot atom'' reactions. 35,40 This was determined by separate measurements with 20% O 2 in the target cell, which completely depolarises all muons that stop in the gas due to repeated electron spin-flip exchange (SE) encounters of Mu with O 2 .…”

Section: Target Environment and Lsr Signalsmentioning

confidence: 67%

“…35 Our TF measurements of the Dia amplitude do not separate contributions due to muon stops in the target walls from the fraction formed in the gas, the latter due to muon molecular ions 37,41 as well as to ''hot atom'' reactions. 35,40 This was determined by separate measurements with 20% O 2 in the target cell, which completely depolarises all muons that stop in the gas due to repeated electron spin-flip exchange (SE) encounters of Mu with O 2 . 42 From this measurement, the muon asymmetry from the walls was found to be B0.03, depending on the stopping environment, and using this adjusted value we obtain excellent agreement for A Mu (and hence f Mu ) with earlier results.…”

Section: Target Environment and Lsr Signalsmentioning

confidence: 67%

“…5,6 In contrast to Mu + CH 4 , as outlined above, to the best of our knowledge neither similar detailed calculations of the Mu + C 2 H 6 reaction rate, in comparison with the experiment, 28,31 nor, of particular interest here, Mu + C 3 H 8 , have been reported. Hot atom reaction yields of Mu with methane and propane are known, 35 but, until the present study, no thermal rates for the Mu + C 3 H 8 reaction in the gas phase have been reported. The Mu + C 3 H 8 rate was also expected to be too slow near RT for a standard TF-mSR technique to be viable, providing motivation as well then for the present, essentially ''proof-of-principle'', measurement of the rate constant for this reaction at 300 K by the technique of diamagnetic RF-resonance (RF-mSR), the first measurement of its kind for a slow Mu reaction.…”

mentioning

confidence: 65%

“…42 From this measurement, the muon asymmetry from the walls was found to be B0.03, depending on the stopping environment, and using this adjusted value we obtain excellent agreement for A Mu (and hence f Mu ) with earlier results. 35,37 The relaxation of the precessing Mu amplitude shown in Fig. 1b is a background effect (l b = 0.36 AE 0.03 ms À1 ), mainly due to field inhomogeneity in the TF environment, DB/B B 12%, arising from the extended stopping distribution of muons in the gas.…”

Section: Target Environment and Lsr Signalsmentioning

confidence: 98%

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Rate constants for the slow Mu + propane abstraction reaction at 300 K by diamagnetic RF resonance

Fleming

Cottrell

McKenzie

et al. 2015

Phys. Chem. Chem. Phys.

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The study of kinetic isotope effects for H-atom abstraction rates by incident H-atoms from the homologous series of lower mass alkanes (CH4, C2H6 and, here, C3H8) provides important tests of reaction rate theory on polyatomic systems. With a mass of only 0.114 amu, the most sensitive test is provided by the rates of the Mu atom. Abstraction of H by Mu can be highly endoergic, due to the large zero-point energy shift in the MuH bond formed, which also gives rise to high activation energies from similar zero-point energy corrections at the transition state. Rates are then far too slow near 300 K to be measured by conventional TF-μSR techniques that follow the disappearance of the spin-polarised Mu atom with time. Reported here is the first measurement of a slow Mu reaction rate in the gas phase by the technique of diamagnetic radio frequency (RF) resonance, where the amplitude of the MuH product formed in the Mu + C3H8 reaction is followed with time. The measured rate constant, kMu = (6.8 ± 0.5) × 10(-16) cm(3) s(-1) at 300 K, 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.

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Section: Target Environment and Lsr Signalsmentioning

confidence: 67%

Section: Target Environment and Lsr Signalsmentioning

confidence: 67%

mentioning

confidence: 65%

Section: Target Environment and Lsr Signalsmentioning

confidence: 98%

See 2 more Smart Citations

Rate constants for the slow Mu + propane abstraction reaction at 300 K by diamagnetic RF resonance

Fleming

Cottrell

McKenzie

et al. 2015

Phys. Chem. Chem. Phys.

Self Cite

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“…In eqn. (7), j is a characteristic distance over which the adiabatic potentials change substantially, *V is the splitting of the adiabatic potential sheets, is an e †ective average velocity for the u n nuclear motion, and j, *V , and all depend on the nuclear u n coordinates. The exponent in eqn.…”

Section: Isotope Dependence Of Non-adiabatic Behaviourmentioning

confidence: 99%

A classical-path surface-hopping study of Mu, H and T hot-atom collisions with F2

Jakubetz¹,

Connor²,

Kuntz³

1999

Phys. Chem. Chem. Phys.

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The collision dynamics of processes pertinent to the hot-atom chemistry of the hydrogen isotopes Mu, H and T with are explored using mixed quantumÈclassical techniques. We use classical-path surface-hopping and F 2 pure classical-path multi-surface trajectory methods with a set of 14 coupled potential energy surfaces (PESs) from a diatomics-in-molecules (DIM) model. We compare with results from the standard quasiclassical trajectory (QCT) method applied to the electronic ground state surface of the same DIM model. We compute reaction-and dissociation cross sections for centre-of-mass collision energies ranging from threshold to 20 eV. In order to quantify the notion of electronic non-adiabaticity we introduce various cross sections measuring electronically non-adiabatic processes. We Ðnd that non-adiabatic e †ects give rise to pronounced changes in the dynamics of the system. In particular, collision-induced dissociation of by Mu is an essentially Mu ] F 2 F 2 electronically non-adiabatic process, proceeding efficiently by a mechanism involving transitions to excited repulsive PESs. In contrast, QCT calculations on the electronic ground state surface predict vanishingly small dissociation cross sections. We also discuss some consequences of this behaviour for simulations of Mu ] F 2 Mu hot-atom chemistry.

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