Acetylene emission from vibrationally excited

Electronic excitation from atom-transfer reactions appears to be relatively uncommon, with most such reactions producing chemiluminescence from vibrationaHy excited ground states (188—191). Examples include reactions of oxygen atoms with carbon disulfide (190), acetylene (191), or methylene (190), all of which produce emission from vibrationaHy excited carbon monoxide. When such reactions are carried out at very low pressure (13 mPa (lO " torr)), energy transfer is diminished, as with molecular beam experiments, so that the distribution of vibrational and rotational energies in the products can be discerned (189). Laser emission at 5 p.m has been obtained from the reaction of methylene and oxygen initiated by flash photolysis of a mixture of SO2, 2 2 6 (1 )-... 

Ketenyl radical (27) is a species involved both in ketene formation and in ketene reactions, and may be formed by hydrogen atom abstraction from ketene. Ethoxy-acetylene is a thermal source of ketene and forms ketenyl radical by 193 nm photolysis in helium, argon, or xenon, with time-resolved IR emission spectroscopy used to examine the lowest quartet state of the radical. The radical with 1785 36 cm for the fundamental transition of the V2 asym-CCO stretch was observed in helium while CO did not form in this medium, but in Ar or Xe vibrationally excited CO was observed, suggesting rapid coUision-induced intersystem crossing occurred due to a heavy-atom effect (Eqn (4.17)). The presumed product CH formed with CO was not however observed and the expected stretching frequencies would be quite weak. 

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