The Isotopic Efiect of Photobromination of CH₄/CH₂D₂ Induced by Ar⁺ Laser

In the photobromination of CH₄/CH₂D₂, it is recognized that Br₂ is first excited to Br₂^* and then dissociate into two Br atoms. Therefore it is necessary to take into consideration the possibility of Br₂^* taking part in the reaction. According to such a mechanism, the relation of reaction constant λ and laser intensity I is shown to be λ=λ₁I\frac12+λ₂I. Experiment shown that λ₂I is the dominant term. It is found experimentally that at T=423K, 455K and 471K, the ratios of the reaction constants of CH₄ and CH₂D₂ are respectively λ_H/λ_D=1.9, 1.65, 1.65. The constant λ is found to obey the Arrhenius law, with the activation energy determined to be E_H=17.5 kcal/mole and E_D=18.9 kcal/mole.