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.

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