Details

Autor(en) / Beteiligte

• Fleming, Donald G
• Cottrell, Stephen P
• McKenzie, Iain
• Ghandi, Khashayar

Titel

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

Ist Teil von

• Physical chemistry chemical physics : PCCP, 2015-08, Vol.17 (3), p.1991-1991

Ort / Verlag

England

Erscheinungsjahr

2015

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The study of kinetic isotope effects for H-atom abstraction rates by incident H-atoms from the homologous series of lower mass alkanes (CH 4 , C 2 H 6 and, here, C 3 H 8 ) 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 + C 3 H 8 reaction is followed with time. The measured rate constant, k Mu = (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 + C 3 H 8 , indicating a dominant contribution from quantum tunneling in the Mu reaction, consistent with elementary transition state theory calculations of the k Mu / k H kinetic isotope effect. The rate constant for the slow Mu + propane abstraction reaction has been determined by diamagnetic RF resonance. The curves show simulations of the μSR resonance signal. This study provides an important new test of reaction rate theory for the alkanes.