FORMATION OF TRIPLET CO IN ATOMIC OXYGEN FLAMES OF ACETYLENE AND CARBON SUBOXIDE

Chemiluminescence spectra have been recorded for low-pressure, highly dilute, fuel-lean atomic oxygen flames of C2H2 and C3O2; under typical flame conditions the total pressure was 0.83 Torr with 1.1 mTorr of O atoms, 0.44 mTorr of O-2, 0.20 mTorr of fuel, and the balance Ar. Spe ctral coverage was complete from 183 to 1500 nm for C2H2, and from 183 to 885 nm for C3O2 Strong CO a --> X Cameron band emission was found to be the dominant feature of the chemiluminescence signature from 190 to 260 nm for C2H2 oxidation under these conditions, with distinct bu t relatively minor CO A --> X fourth positive emission between 185 and 195 nm. There is strong emission from higher tripler states of CO thr oughout the visible and near-IR, with CO e --> a, d --> a, and a' --> a emission features observed. Nearly identical CO emission spectra wer e obtained for both C2H2 and C3O2 fuels, which indicates that for both fuels the source of electronically excited CO is the C2O + O reaction . Quantification of emission yields for the four triplet electronic st ates of CO observed here indicates that little or no CO(a) is formed d irectly, rather its population results from radiative emission from hi gher triplet states. Approximately 70% of the triplet CO formed direct ly from the C2O + O reaction is in the a' state, which had not been pr eviously identified in this system.