ESR Study of the Kinetic Isotope Effect in the Reaction of H and D Atoms with CH4

ESR atom detection has been employed to determine the kinetic isotope effect involved in the reactions: H+CH4→H2+CH3, D+CH4→HD+CH3.New data were obtained for Reaction (1) leading to a slightly revised value for k1 of (6.25 ± 2.00) × 1013exp− (11 600 ± 150) / RT in units of cm3 mole−1·sec−1. Assuming that the ratio of pre-exponential factors for Reactions (1) and (2) is 1.38 we compute a value for k2 of (4.5 ± 2.0) × 1013exp− 11 100 ± 150) / RT cm3 mole−1·sec−1. The observed kinetic isotope effect is compared with those calculated from absolute rate theory using the semiempirical Sato potential energy surface, or that obtained from the empirical bond-energy–bond-order (BEBO) method. These two methods give equally good predictions of the value of k1 / k2. Application of a one-dimensional tunnel correction results in poorer agreement between theory and experiments.