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Hydrogen atoms in a methane-air Bunsen-type flame were detected by the flame-in-cavity ESR method. The addition of a halogenated compound to the secondary air was found to reduce the H-atom concentration linearly with an increase in the additive concentration. The eight halogenated compounds examined showed an increased effectiveness in scavenging H atoms in this order; HCl<CF2Cl2<CHCl3<CH3Cl<CH2Cl2<CFCl3<CCl4<CH3Br. This chemical effect of the halogenated compounds on the combustion reactions agrees well with the inhibitor index for these compounds.

Labile intermediates in a premixed methanol-air flame burning freely at atmospheric pressure have been studied by probe sampling and EPR detection. H, 0, and OH have been detected at a pressure of 0.45 torr in the EPR cavity. It was found that H and 0 atoms have their maximum concentrations in the inner flame region within 1 mm from the burner mouth, while the OH concentration slowly increases in the outer flame region to reach a maximum at about 8 mm from the burner mouth. The slow increase in OH concentration is attributed to the reaction H + O2 -OH + 0 effectuated by diffusion of O2 from the surrounding air into the flame. Addition of H 2 0 reduced the 0 atom concentration and increased the OH radical concentration in the inner flame region. The reaction 0 + H 2 0 -20H is suggested as an explanation. Addition of HBr gave additional signals from Br and was found to reduce the H, 0, and OH concentrations in the flame. It also caused the flame to shrink probably as a result of H atom deficiency in the inner flame region leading to insufficient generation of 0 and OH in the outer flame region. About 70% of the bromine was found to exist in the atomic form.

The cyclohexane cation has been studied theoretically using ab initio MO-LCAO-UHF calculations, as well as experimentally, by means of low-temperature ESR measurements in a CF3CCl3 matrix between 4 and 140 K. It is found that the most stable conformation of the free cation is a distorted chair conformation with Cs symmetry, with one carbon atom being separated from the others by bonds that are approximately 0.1 Å larger than the remaining C–C bonds. The symmetrical chair conformation of C2h symmetry is predicted by the calculations to lie approximately 6 kcal/mol above this lowest state. The possibility of a change of ground state because of matrix interactions is discussed in connection with the temperature dependence of the spectra.

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