Abstract: Hydrogen atoms produced in the radiolysis of water vapor were used to determine the kinetic isotope effects for the reactions He+ RH (RD)-+ H2 (HD)+ R.[kH (kD)], where RH is a perprotiated alkane and RD is the corresponding perdeuterated alkane. The alkanes studied include a homologous series of cycloalkanes, cyclopentane through cyclododecane, and isobutane, 2, 3-dimethylbutane, 2, 3, 4-trimethylpentane, and neopentane. The results ...