Reaction of oxygen atoms with acetylene

In the low temperature reaction of oxygen atoms with acetylene at pressures in the torr range, chemiluminescent emission is observed from one or more electronically excited states of CO, CH, C2, OH and CHO. In none of these cases is the mechanism well established, so we will only mention briefly some recent work. 

Emission from CO A(lIJ), the fourth positive bands, has been observed in the vacuum ultraviolet267,268 and emission from the triplet states d(3A) and e (3E) appears to arise from the same excitation process268, possibly O+C20 - CO +CO. 

The mechanism of chemi-ionization and of CH( 4 2A) emission has been studied in considerable detail269,331 but it was not possible to decide on a unique mechanism for the emission process. Observed rotational distributions in the CH (A 2 A) state have been interpreted in terms of rotational relaxation270 but the uncertainty in the excitation mechanism renders such an enterprise somewhat ambiguous. 

Emission of the hydrocarbon flame bands, due to HCO, has recently been studied, along with chemi-ionization271. Again the mechanism is uncertain. 

Rotational and vibrational distributions, as well as relative intensities of bands emitted by different molecules, have been surveyed by Krishnamachari and Broida272. They worked with 0 + C2H2 and also studied effects of added 02. 

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Kinetic data on the reaction of oxygen atoms.with acetylenic compounds is reported in Table 25. It should be noted that the reaction with acetylene, for which there is considerable data, is much slower than the corresponding reaction with ethylene. The reactivity of ethylene is about five times greater than that of acetylene. This contrasts with bromine atom addition in which the reactivity of acetylene is slightly greater than that of... 

A. Fontijn and G. L. Baughman, Chemi-ionization in the room-temperature reaction of oxygen atoms with acetylene, J. Chem. Phys. 38, 1784-1785 (1963). 

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