The kinetic isotope effect in the photochlorination of methane

The kinetic isotope effect for the photochemically initiated chlorination of methane-d2 has been determined. The value is kH/kD  12·1 at 0°C., and the variation with temperature is given by kH/kD  1·09 exp (1300/RT. The results are considered in terms of a semiempirical potential energy surface, and the general subject of the magnitudes of primary kinetic isotope effects is discussed.