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 (k(2) ) and to examine the contribution of the roaming isomerization pathway in nitromethane decomposition. The resultant rate constant can be expressed as k(2) = (9.3 +/- 1.8) x 10(-10)(T/K)(-0.5) cm(3) 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.