Kinetic Study in a Microwave-Induced Plasma Afterglow of the Cu(2S) Atom Reaction with CH3Cl in the Temperature Range 389−853 K

Abstract

A kinetic study of the reaction Cu + CH3Cl CuCl + CH3 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 the experimental parameters such as the hydrogen content, sublimation temperature of CuCl pellet, and reactor pressure on k1 has been verified. The rate constant k1 was measured at temperatures between 389 and 853 K, which resulted in the Arrhenius expression k1 = (1.73 ± 0.45) × 10-11 exp(−34.7 ± 1.2 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) = ATn exp(−E/RT). Meaningful kinetic parameters can only be derived when n is fixed. A value of n = 2.15 was obtained using transition state theory combined with ab initio molecular orbital calculations. In that case the activation barrier of the reaction is lowered to 24.8 kJ mol-1. The measured values of k1 as a function of temperature can best be calculated over the 389−853 K range by the expression log k1(T) = −21.22 − 10.99(log T) + 3.30(log T)2.