Electron spin resonance (ESR) investigation of the structure of methyl radical trapping sites in methanol glass

1987 ◽  
Vol 86 (12) ◽  
pp. 6622-6630 ◽  
Author(s):  
T. Doba ◽  
K. U. Ingold ◽  
A. H. Reddoch ◽  
W. Siebrand ◽  
T. A. Wildman
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Methyl Radical ◽  
Radical Trapping ◽  
Spin Resonance ◽  
Trapping Sites

Electron spin resonance study of the reaction of hydrogen atoms with methane

1994 ◽  
Vol 72 (3) ◽  
pp. 600-605 ◽  
Author(s):  
Paul-Marie Marquaire ◽  
Ashok Ghose Dastidar ◽  
Kim C. Manthorne ◽  
Philip D. Pacey
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Activation Barrier ◽  
Heat Of Formation ◽  
State Theory ◽  
Electron Spin Resonance Study ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Atom Concentration ◽  
Spin Resonance

The reaction: H + CH4 → CH3 + H2 has been investigated in a flow system between 348 and 421 K. Hydrogen atoms were generated in a microwave discharge, introduced to the reactor through a movable injector, and monitored by electron spin resonance. After an initial decay attributed to reaction with impurity, the hydrogen atom concentration decayed in a pseudo-first-order manner. Ethane was detected by gas chromatography, consistent with its formation by the following reaction: 2CH3 → C2H6. The amount of ethane formed at 421 K was only 0.015 times the amount of hydrogen atoms reacting. Most methyl radicals were assumed to have been removed by the process: H + CH3 + M → CH4 + M. Because of this process, two hydrogen atoms were removed each time the title reaction occurred. Applying this stoichiometric factor, the rate constant for the elementary reaction was calculated to be 2.5 × 103 L mol−1 s−1 at 348 K, increasing to 2.0 × 104 L mol−1 s−1 at 421 K. Most of the previous discrepancy between kinetics and thermochemistry has been eliminated; the exothermicity at 0 K was reduced to 0.8 ± 0.4 kJ mol−1, which corresponds to a standard heat of formation of the methyl radical of 145 kJ mol−1. Properties of the activation barrier have been inferred from the experimental data with the aid of transition state theory. The fitted barrier height was 63 ± 1 kJ mol−1, the average of five low-frequency vibrational term values was 640 ± 30 cm−1, and the characteristic tunnelling temperature was 500 ± 30 K.

Sign in / Sign up

Export Citation Format

Share Document