Temperature Effect on Selective Tunneling Abstraction Reaction by H Atoms in Neopentane−Alkane Mixtures at 4−100 K

Abstract

When H atoms are produced by the photolysis of HI or the radiolysis of neo-C5H12 in the neo-C5H12−i-C4H10(2 mol %) mixtures above 40 K, the H atoms react selectively with the solute i-C4H10. The selective reaction is suppressed below 30 K. The reactions have been studied by electron spin resonance and electron spin echo measurements at 4−100 K. The drastic temperature effect on the reaction by H atoms suggests that the H atoms concerned are not hot atoms, but thermal atoms. The thermal H atoms react with the solute alkane by quantum tunneling at low temperature. Temperature effects on the ESR spectra and the spin−lattice relaxation times of the solvent neo-C5H11 radicals and the solute t-C4H9 radicals indicate that local motions of the solute i-C4H10 molecules take place above 40 K, while motions of the solvent neo-C5H12 molecules are severely restricted even at 100 K. It is concluded that the local motions of the solute i-C4H10 assist the tunneling abstraction reaction by H atoms, resulting in the selective reaction with the solute above 40 K.

7 Radiation chemistry

“…It is concluded that the local motions of the solute assist the tunnelling abstraction by H atoms. 283 In 1,2-dimethylcyclohexane irradiated at 77 K, the dimethyl-cyclohexene radical cation is formed by a cis^trans stereoselective H 2 detachment from the primary radical cation occurring only for the cis-isomer. 284 In MCH and in binary matrices MCH^isopentane at 6^77 K, the pulse radiolysis of CFCl 3 solutions leads to an ion pair CFCl 3 ÁÁÁ Cl À (l max 430 nm).…”