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: $$\mathrm{H}+\mathrm{CH}\text{4→H2+}\mathrm{CH}\text{3,}$$ $$\mathrm{D}+\mathrm{CH}\text{4→}\mathrm{HD}+\mathrm{CH}\text{3.}$$ New data were obtained for Reaction (1) leading to a slightly revised value for $k_1$ of ${\text{(6.25\hspace{0.17em}±\hspace{0.17em}2.00) \hspace{0.17em}×\hspace{0.17em} 10}}^{13}\exp \text{[−\hspace{0.17em}(11 600\hspace{0.17em}±\hspace{0.17em}150)\hspace{0.17em}/\hspace{0.17em}RT]}$ 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 $k_2$ of ${\text{(4.5\hspace{0.17em}±\hspace{0.17em}2.0) \hspace{0.17em}×\hspace{0.17em} 10}}^{13}\exp \text{[−\hspace{0.17em}11 100\hspace{0.17em}±\hspace{0.17em}150)\hspace{0.17em}/\hspace{0.17em}RT]}$ 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 $k_1{\mathrm{\hspace{0.17em}/\hspace{0.17em}k}}_2$ . Application of a one‐dimensional tunnel correction results in poorer agreement between theory and experiments.