Journal of Physical Chemistry A vol:102 issue:8 pages:1349-1355
A kinetic study of the reactions Cu + CH3Br --> CuBr + CH3 (k(1)) and Cu + CH3I --> CuI + CH3 (k(2)) 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 k(1) and k(2) has been verified. The rate constant k(1) was measured at temperatures between 300 and 804 K, which resulted in the Arrhenius expression k(1) = (1.7 +/- 0.2) x 10(-11) exp[(-8.2 +/- 0.5 kJ mol(-1))/RT] cm(3) molecule(-1) s(-1). Since the Arrhenius plot shows a slight curvature, the values of k(1) were also fitted to the modified Arrhenius equation k(T) = A T-n exp(-E/RT). Meaningful kinetic parameters can only be derived when n is fixed. The measured values of k(1) can be best described as a function of temperature over the 300-804 K range by the expression log k(1)(T) = + 223.6669 - 264.2058(log T) + 97.7693(log T)(2) - 11.9244(log T)(3). Th, Arrhenius expression for rate constant k(2) is k(2) = (7.9 +/- 0.5) x 10(-11) exp[(-0.8 +/- 0.2 kJ mol(-1))/RT] cm(3) 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.