KINETICS AND PRODUCTS OF THE REACTION OF THE VINOXY RADICAL WITH O-2

The kinetics and products of the C2H3O (vinoxy) + O-2 reaction have been studied as a function of pressure by employing excimer laser photolysis in combination with cavity ring-down spectroscopy. The reaction rate constants were determined by monitoring the rate of disappearance of the vinery radical by its absorption at 347.6 nm. The bimolecular rate constants were measured over the major portion of the transition region from the low-pressure to the high-pressure limits (2.5 Torr less than or equal to P less than or equal to 400 Torr) and were well fit by the falloff expression of Tree with coefficients k(0) = (1.6 +/- 0.3) x 10(-30) cm(6) molecule(-2) s(-1), k(infinity) = (1.9 +/- 0.2) x 10(-13) cm(3) molecule(-1) s(-1), and F-c = 0.50 +/- 0.06. Glyoxal was identified as a product of the reaction; however, its rate of appearance (on the order of 900 mu s) was not comparable to the rate of disappearance of the vinery radical (faster than 90 mu s). Varying the third body carrier gas from N-2 to SF6 or CF4 had no obvious effect on the glyoxal appearance rates. The disparity between the rate of disappearance of the reactant and the rate of appearance of glyoxal suggests that glyoxal is a secondary product of the reaction of the vinery radical with O-2 that may involve the breakup of long-lived O2C2H3O adducts (the estimated lifetime of the adduct was 900 mu s). The absorption cross section of glyoxal at 440.7 nm was determined to be 4.6 x 10(-19) cm(2)/molecule. The glyoxal yield was 0.15 +/- 0.05 per vinoxy radical formed. Preliminary study indicated that formaldehyde was another available reaction channel. Possible reaction mechanisms are discussed.