Methyl chloride formation by gas phase thermal chlorine atom reaction with methyl iodide and methyl bromide

Thermal chlorine atoms react with gaseous CH 3 I and CH 3 Br at 295K to produce CH 3 Cl with yields of 8.6% and 0.6%, respectively. The studies utilized radioactive 38 Cl formed by the 37 Cl (n,γ) 38 Cl nuclear reaction in gaseous CClF 3 at pressures from 760 to 4,000 torr. The initially energetic 38 Cl atoms are thermalized by multiple inelastic collisions with CClF 3 prior to reaction with the methyl halide. The reaction rate constant for thermal chlorine attack on CH 3 Br to form CH 3 Cl at 295K and 1–5 atmospheres pressure is (2.0±0.5) × 10 −15 cm³ molecule −1 s −1 . The substitution of Cl for Br/I in a methyl halide molecule cannot be a significant source of atmospheric CH 3 Cl because of its abundance from other sources. However, the replacement of I by Cl in other iodohalocarbons might in some cases provide a marker for the presence of atomic chlorine.