Hydrocarbon/oxygen mixture seeded with nitrogen dioxide were ignited by xenon flash photolysis. Combustion appeared uniformly throughout the entire volume. C2, CH and OH radical emissions were measured under the several initial pressures and equivalence ratios. Two different emission peaks of C2 and CH were found depending on initial pressure and equivalence ratio. OH emission intensity varies smoothly with time, and increased linearly with pressure. The second emission peaks of C2 and CH could count among the thermally exited emission because of the matched OH emission peaks. The first ones were considered to he the chemically exited emissions. An attempt is made to explain that the two emission peaks appear by the reaction : CH2→C*2, CH* (chemical excltation)→C*2, CH* (thermal excitation) associated with polymerization/destruction.