Computational Study on the Kinetics and Mechanism for the Unimolecular Decomposition of C_6H_5NO_2 and the Related C_6H_5 + NO_2 and C_6H_5O + NO Reactions

摘要

The kinetics and mechanisms for the unimolecular dissociation of nitrobenzene and related association reactions C_6H_5 + NO_2 and C_6H_5O + NO have been studied computationally at the G2M(RCC,MP2)level of theory in conjunction with rate constant prediction with multichannel RRKM calculations.Formation of C_6H_5 + NO_2 was found to be dominant above 850 K with its branching ratio > 0.78,whereas the formation of C_6H_5O + NO via the C_6H_5ONO intermediate was found to be competitive at lower temperatures,with its branching ratio increasing from 0.22 at 850 K to 0.97 at 500 K.The third energetically accessible channel producing C_6H_4 + MONO was found to be uncompetitive throughout the temperature range investigated,500-2000 K.The predicted rate constants for C_6H_5NO_2-> C_6H_5 + NO_2 and C_6H_5O + NO - C_6H_5ONO under varying experimental conditions were found to be in good agreement with all existing experimental data.For C_6H_5 + NO_2,the combination processes producing C_6H_5ONO and C_6H_5NO_2 are dominant at low temperature and high pressure,while the disproportionation process giving C_6H_5O + NO via C_6H_5ONO becomes competitive at low pressure and dominant at temperatures above 1000 K.