Measuring the rate constant of azomethane decomposition in shock waves

The rate constant of azomethane decomposition in argon was measured at temperatures of 820 to 1400 K, pressures of 0.25 to 7.5 atm, and initial azomethane concentrations of 40 to 2000 ppm. The amount of azomethane reacted was estimated as UV light absorption at the vacuum UV boundary (λ = 198 nm), and the concentration of (dot CH_3 ) radicals resulting from azomethane decomposition was monitored as absorption at λ = 216 nm. The observed temperature dependence of the azomethane decomposition rate constant, k ₁ ^app = 10^11.3exp(?33.5/RT)s^?1, is in good agreement with the literature. The low values of the activation energy and preexponential factor are unnatural for classical monomolecular decomposition. This confirms the assumption that azomethane decomposition at high temperatures takes place via a concerted mechanism.