Decomposition of Nitromethane in Shock Waves: The Primary Stage and the Kinetics of Decomposition at Pressures of about 40 atm

The kinetics of nitromethane (NM) decomposition and the observed rate constant of the process were measured behind reflected shock wave using absorption spectroscopy at lambda = 230 nm, temperatures of 1060 to 1350 K, pressure of similar to 40 atm, and initial reactant concentration within 30-100 ppm. It was observed that, at the initial stage, nitromethane decomposes exponentially, without autoacceleration. The results of numerical simulations with the help of three most known kinetic schemes of nitromethane decomposition proved to be in close to agreement with our experimental data over the entire temperature range covered. It was demonstrated that the measured rate constant is identical to the rate constant of the dissociation CH3NO2 -> CH3 + NO2. The temperature dependence of k(1) was approximated by the Arrhenius formula k(1) = 2.57 x 10(14) exp(-52.85/RT) s(-1) (activation energy in kcal/mol), which suggests that the nitromethane dissociation proceeds in the falloff pressure region.