A measurement of the yield of carbon monoxide from the reaction of methyl radicals and oxygen atoms

We have determined the branching fraction for the production of CO from the reaction of methyl radicals and O(P-3) atoms at room temperature to be 0.1 8 +/- 0.04 at T = 296 K. The measurement was made by determining the concen tration of CO using tunable infrared diode laser absorption. Methyl radical s and O atoms were prepared by 193-nm excimer laser photolysis of acetone a nd SO2. CO produced directly from acetone photolysis was distinguished from that generated by the radical-radical reaction by using acetone labeled wi th C-13 only on the methyl groups. The result is in excellent agreement wit h another determination of the CO branching fraction made using time-of-fli ght mass spectrometry.