UV to Near-IR CO Emissions from O + C2H2 and O + C3O2 Flames at Low Pressure and High Temperature

Emission spectra from C2H2 + O flames have been studied in a low-pressure, fast flow discharge system under highly dilute, fuel-lean conditions from 295 to 873 K. Our previous work with room-temperature flames has been extended to look for temperature-induced changes in the relative populations of triplet CO(a), (a ‘), (d), and (e) reaction products by observing chemiluminescent emission in the 185−900 nm wavelength region. The effect of temperature on the relative yields of the CO triplet states was small, and the production rates increased linearly with the temperature-dependent rate of the initial O + C2H2 reaction step. To test the importance of C2O as a major pathway to triplet state CO, similar experiments were performed on C3O2 + O flames. The relative yields of the CO triplet states showed little temperature dependence; however, the overall triplet production rate increased much faster with temperature than the initial O + C3O2 reaction and may be related to temperature variation of the branching ratio yielding C2O in the initial reaction. Relative vibrational level populations were determined in the CO triplet states and were slightly hotter in C3O2 flames than in C2H2 flames throughout the temperature range.