화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.117, No.51, 14019-14027, 2013
Temperature Dependence of the OH- + CH3I Reaction Kinetics. Experimental and Simulation Studies and Atomic-Level Dynamics
Direct dynamics simulations and selected ion flow tube (SIFT) experiments were performed to study the kinetics and dynamics of the OH-+ CH3I reaction versus temperature. This work complements previous direct dynamics simulation and molecular beam ion imaging experiments of this reaction versus reaction collision energy (Xie et al. J. Phys. Chem. A 2013, 117, 7162). The simulations and experiments are in quite good agreement. Both identify the S(N)2, OH- + CH3I > CH3OH + I-, and proton transfer, OH-+ CH3I CH2I-+ H2O, reactions as having nearly equal importance. In the experiments, the 5N2 pathway constitutes 0.64 +/- 0.05, 0.56-4-0.05, 0.51 + 0.05, and 0.46 + 0.05 of the total reaction at 210, 300, 400, and 500 K, respectively. For the simulations this fraction is 0.56 + 0.06, 0.55 +/- 0.04, and 0.50 +/- 0.05 at 300, 400, and 500 K, respectively. The experimental total reaction rate constant is (2.3 +/- 0.6) x 10(-9), (1.7 +/- 0.4) X 10(-9), (1.9 +/- 0.5) X 10-9, and (1.8 +/- 0.5) X 10-9 cm(3)s-1 at 210, 300, 400, and 500 K, respectively, which is approximately 25% smaller than the collision capture value. The simulation values for this rate constant are (1.7 +/- 0.2) X 10-9, (1.8 +/- 0.1) x 10-9, and (1.6 + 0.1) X 10(-9) cm(3)s I at 300, 400, and 500 K. From the simulations, direct rebound and stripping mechanisms as well as multiple indirect mechanisms are identified as the atomic-level reaction mechanisms for both the S(N)2 and proton-transfer pathways. For the S(N)2 reaction the direct and indirect mechanisms have nearly equal probabilities; the direct mechanisms are slightly more probable, and direct rebound is more important than direct stripping. For the proton-transfer pathway the indirect mechanisms are more important than the direct mechanisms, and stripping is significantly more important than rebound for the latter. Calculations were performed with the OW quantum number J equal to 0, 3, and 6 to investigate the effect of OH-rotational excitation on the OH- + CH3I reaction dynamics. The overall reaction probability and the probabilities for the S(N)2 and protontransfer pathways have little dependence on J. Possible effects on the atomistic mechanisms were investigated for the S(N)2 pathway and the probability of the direct rebound mechanism increased with J. However, the other atomistic mechanisms were not appreciably affected by