Kinetic Study in a Microwave-Induced Plasma Afterglow of the Cu (2S) Atom Reaction with CH3Br at Temperatures between 300 and 804 K and with CH3I between 300 and 696 K

Abstract

A kinetic study of the reactions Cu + CH3Br → CuBr + CH3 (k1) and Cu + CH3I → CuI + CH3 (k2) has been carried out in a fast-flow reactor. The gas-phase copper atoms were generated using the microwave-induced plasma (MIP) afterglow technique. Atomic absorption spectroscopy at 327.4 nm was used as the detection technique. The influence of experimental parameters such as the hydrogen content, sublimation temperature of the CuCl pellet, and reactor pressure on k1 and k2 has been verified. The rate constant k1 was measured at temperatures between 300 and 804 K, which resulted in the Arrhenius expression k1 = (1.7 ± 0.2) × 10-11 exp[(−8.2 ± 0.5 kJ mol-1)/RT] cm3 molecule-1 s-1. Since the Arrhenius plot shows a slight curvature, the values of k1 were also fitted to the modified Arrhenius equation k(T) = A Tn exp(−E/RT). Meaningful kinetic parameters can only be derived when n is fixed. The measured values of k1 can be best described as a function of temperature over the 300−804 K range by the expression log k1(T) = +223.6669 − 264.2058(log T) + 97.7693(log T)2 − 11.9244(log T)3. The Arrhenius expression for rate constant k2 is k2 = (7.9 ± 0.5) × 10-11 exp[(−0.8 ± 0.2 kJ mol-1)/RT] cm3 molecule-1 s-1 between 300 and 696 K. The obtained results will be discussed in terms of the electron-jump model, and some reactivity/structure relations will be presented.