Reaction Dynamics of CH₃+ HBr → CH₄+ Br at 150-1000 K

Abstract

The kinetics of the radical-polar molecule reaction CH 3 + HBr → CH 4 + Br has been studied at temperatures between 150 and 1000 K using classical dynamics procedures. Potential energy surfaces constructed using analytical forms of inter-and intramolecular interaction energies show a shallow well and barrier in the entrance channel, which affect the collision dynamics at low temperatures. Different collision models are used to distinguish the reaction occurring at low-and high-temperature regions. The reaction proceeds rapidly via a complex-mode mechanism below room temperature showing strong negative temperature dependence, where the effects of molecular attraction, H-atom tunneling and recrossing of collision complexes are found to be important. The temperature dependence of the rate constant between 400 and 1000 K is positive, the values increasing in accordance with the increase of the mean speed of collision. The rate constant varies from 7.6 × 10 −12 at 150 K to 3.7 × 10 −12 at 1000 K via a minimum value of 2.5 × 10 −12 cm 3 molecule −1 s −1 at 400 K.

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