Thermal Decomposition of Nitromethane and Reaction between CH₃ and NO₂

The thermal decomposition of gaseous nitromethane and the subsequent bimolecular reaction between CH₃ and NO₂ have been experimentally studied using time-resolved cavity-enhanced absorption spectroscopy behind reflected shock waves in the temperature range 1336-1827 K and at a pressure of 100 kPa. Temporal evolution of NO₂ was observed following the pyrolysis of nitromethane (diluted to 80-140 ppm in argon) by monitoring the absorption around 400 nm. The primary objectives of the current work were to evaluate the rate constant for the CH₃ + NO₂ reaction (k₂) and to examine the contribution of the roaming isomerization pathway in nitromethane decomposition. The resultant rate constant can be expressed as k₂ = (9.3 ± 1.8) × 10^-10(T/K)^-0.5 cm³ molecule^-1 s^-1, which is in reasonable agreement with available literature data. The decomposition of nitromethane was found to predominantly proceed with the C-N bond fission process with the branching fraction of 0.97 ± 0.06. Therefore, the upper limit of the branching fraction for the roaming pathway was evaluated to be 0.09.