Vacuum-Ultraviolet Chemiluminescence in the Reaction of Atomic Oxygen with Acetylene

Vacuum-ultraviolet emission from the reaction of atomic oxygen with acetylene was investigated spectrographically and with photoionization detectors. The spectrum was observed at wavelengths above 1400 Å and consisted entirely of bands belonging to the fourth positive system of CO. At short wavelengths, the intensity declines rapidly, but radiation was detected with photoionization detectors filled with xylene (1425–1475 Å), NO (1100–1340 Å), and CS2 (1100–1260 Å). The high-energy limit of the emission is, correspondingly, greater than 226 kcal/mole or almost 10 eV. The dependence of the intensity on initial reactant and third-body concentrations was investigated and compared with similar concentration-dependence data for the intensity of the CH band at 4300 Å. The results show that the vacuum-ultraviolet CO emission cannot be produced by either third-body recombination of carbon and oxygen atoms or by the reaction of atomic oxygen with excited CH radicals in the A2Δ state. The reaction proposed by Becker and Bayes O+C2O→CO (A 1Π)+CO (X 1Σ)can explain the observed emission if it is assumed that a fraction of the reaction C2O radicals are vibrationally excited.