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

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 + HONO 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.