Electron Spin Resonance of Hydrogen Atoms in CaF2

1962 ◽  
Vol 127 (6) ◽  
pp. 1892-1912 ◽  
Author(s):  
J. L. Hall ◽  
R. T. Schumacher
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Hydrogen Atoms ◽  
Spin Resonance

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.

Electron Spin Resonance of Hydrogen Atoms in CaF2

1963 ◽  
Vol 131 (6) ◽  
pp. 2839-2839 ◽  
Author(s):  
J. L. Hall ◽  
R. T. Schumacher
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Hydrogen Atoms ◽  
Spin Resonance

Detection of trapped electrons in organic glasses after gamma irradiation at 4.2 °K by electron spin resonance spectroscopy

1967 ◽  
Vol 45 (22) ◽  
pp. 2723-2727 ◽  
Author(s):  
D. R. Smith ◽  
J. J. Pieroni
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Dipole Interaction ◽  
Necessary Condition ◽  
Resonance Spectroscopy ◽  
Hydrogen Atoms ◽  
Trapped Electrons ◽  
Organic Glasses ◽  
Spin Resonance ◽  
Gamma Irradiated

Several organic glasses which are known to form trapped electrons when gamma irradiated at 77 °K have been irradiated at 4.2 °K and examined by electron spin resonance (e.s.r.) at the same temperature. In each case an absorption is observed which is probably due to trapped electrons. In three cases, the yield of trapped electrons at 4.2 °K seems to be as great as at 77 °K. In one case, a glassy alkane, the yield is enhanced at 4.2 °K. Trapped electrons in ethanol give a narrower e.s.r. line at 4.2 °K than at 77 °K, suggesting less orientation in the solvent cage.Trapped hydrogen atoms are not detected after irradiation at 4.2 °K. Contrary to prediction, hydrogen atoms are also not detected after post-irradiation photolysis of the trapped electrons.The results suggest that electron traps exist prior to irradiation and that molecular orientation via electronic dipole interaction is not a necessary condition for electron trapping. The results do not distinguish between trapping in solvent defects or trapping via electron-induced polarization of molecular orbitals.

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