Publication costs assisted by Faculty of Engineering, Nagoya University H atoms produced by the photolysis of hydrogen halide are efficiently trapped in a xenon matrix at 4 K. The ESR spectrum of the H atoms is very complex, consisting of about 80 satellite lines spread over 214 G. The analysis of the complex spectrum suggests that the H atoms are trapped in a substitutional site in the xenon crystal. When Xe-i-C4H10-HI is UV irradiated at 77 K, H atoms migrate through the matrix and react effectively with the solute i-C4H10, resulting in the formation of C4H9 radicals. A large amount of trapped H atoms are produced in the photolysis of Xe-t-C4H10-HI at 4 K. Upon annealing of the UV-irradiated sample from 4 to 77 K, the amounts of isomeric C4H9 radicals do not increase at all, while H atoms disappear completely. It is concluded that the formation of C4H9 radicals in the photolysis at 77 K is not caused by thermal H atoms, but rather by hot H atoms.

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The selective formation of HD and solute radicals in the radiolysis of n-C10D22 doped with n-C10H22 at 77 K is explained quantitatively by the mechanism of a selective hydrogen-atom-abstraction reaction by D atoms. The selective hydrogen-atom abstraction by H atoms is found also in tetramethylsilane and xenon matrices as well as in the alkane matrix. The rate constants of the abstraction reaction by H atoms are compared with the bond energies of the solvent and solute molecules. The bond energy of the solvent molecule is always higher than that of the solute molecule. Even if the difference in the bond energy between the solvent and the solute is very small, the k(solute)/k(solvent) ratio is quite large. The k(solute)/k(neo-C5H12) ratios for different solutes in a neopentane matrix are not influenced by the differences in the bond energy among the solutes. Since an isotope effect on the selective hydrogen-atom abstraction reaction is small, the effect may diminish the possibility of the quantum mechanical tunneling abstraction by thermal H atoms. The energy loss of hot H atoms in a Xe matrix is discussed.

ESR spectra of γ‐irradiated poly(methyl methacrylate) (PMMA) at 77°K and the effect of additives have been studied. γ‐Irradiation of PMMA containing a small amount of 2‐methyltetrahydrofuran as an additive at 77°K gives MTHF radical. Yields of MTHF radical increase with increasing MTHF concentration and reach a plateau value, and are independent of photobleaching with visible light. Yeilds of polymer radical are reduced by the addition of MTHF. Some elementary processes for the MTHF radical formation are proposed on the basis of the experimental results.

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A selective hydrogen atom abstraction reaction by H atoms, which are produced at 77K by radiolysis of alkane or photolysis of hydrogen halides, has been found in isobutane, 2,2,3,3-tetramethylbutane (TMB), and cyclopropane matrices as well as in the neopentane matrix. The selective hydrogen atom abstraction reaction is caused by H atoms which have initial kinetic energies in the range from 15 to 67 kcal/mol. The reaction is caused also by D atoms. The competitive reaction between c-C6H12 and HI for H atoms has been studied in the radiolysis and photolysis of neo-C5H12–c-C6H12–HI mixture at 77K. The rate constants of these reactions in the neopentane matrix are quite different from those of a thermal H atom reaction, but similar to those of a hot H atom reaction. The importance of the selective hydrogen atom abstraction reaction by H atoms is pointed out in the radical formation in the radiolysis of pure TMB at 77K.