Electron spin resonance studies of radicals condensed from irradiated water vapor: reactions of the radicals

1969 ◽  
Vol 47 (12) ◽  
pp. 2149-2154 ◽  
Author(s):  
P. Wardman ◽  
W. A. Seddon
Keyword(s):  
Electron Spin Resonance ◽  
Water Vapor ◽  
Electron Spin ◽  
Radical Scavengers ◽  
Hydrogen Atoms ◽  
Flow Rates ◽  
Spectroscopic Assignment ◽  
Spin Resonance ◽  
Polycrystalline Ice ◽  
Chemical Evidence

Electrons and hydroperoxyl radicals are trapped in polycrystalline ice after irradiation of water vapor and rapid condensation to 77 °K. Using higher sample flow rates than in the earlier work of Seddon, Smith, and Bindner, the electron spin resonance spectra of the trapped electrons (et−) were obtained in both H2O and D2O ice with negligible interference from the underlying HO2• (DO2•) radicals. Addition of C(NO2)4, H2O2, (CH3)2SO, and O2 as radical scavengers confirmed the earlier prediction that reactions with the radicals do not occur in the vapor phase in this system. The results with C(NO2)4 and H2O2 also provided chemical evidence consistent with the spectroscopic assignment for HO2• (DO2•) radicals. Experiments with added isobutylene suggested that hydrogen atoms are formed (possibly in a post-irradiation reaction during condensation) and are also produced on photobleaching et− at 77 °K.

scholarly journals Electron spin resonance detection of radicals and electrons condensed from water vapor after irradiation with 1 MeV helium ions

1968 ◽  
Vol 46 (10) ◽  
pp. 1747-1754 ◽  
Author(s):  
W. A. Seddon ◽  
D. R. Smith ◽  
P. E. Bindner
Keyword(s):  
Electron Spin Resonance ◽  
Water Vapor ◽  
Electron Spin ◽  
Ion Beam ◽  
Physical Parameters ◽  
Hydrogen Atoms ◽  
Beam Experiment ◽  
Spin Resonance ◽  
Vapor Stream ◽  
Resonance Detection

A stream of water vapor was irradiated in a "crossed-beam" experiment by 1 MeV He+ ions. After traversing the He+ ion beam, the vapor was condensed on a quartz tube at 77°K. The deposit so formed was then isolated under vacuum and transferred to an electron spin resonance (e.s.r.) spectrometer. E.s.r. spectra were observed that arise from species formed as a consequence of radiolysis in the vapor phase. Species trapped in the deposit were identified as HO2 radicals and electrons. Addition of CH3I and N2O gives results which indicate that hydrogen atoms were also formed although they do not become trapped in the deposit.The physical parameters of the experiment have been measured or calculated. These include the pressure and velocity of molecules in the vapor stream, and the time between irradiation and deposition on the cold finger.

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

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
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