Product Study of the Reaction of CH3 with OH Radicals at Low Pressures and Temperatures of 300 and 612 K†

Abstract

The product distribution for the title reaction was studied using our time-of-flight mass spectrometer (TOFMS) connected to a tubular flow reactor. The methyl and hydroxyl radicals were produced by an excimer laser pulse (lambda = 193 nm) photolyzing acetone and nitrous oxide in the presence of excess water or hydrogen. Helium was used as the bath gas; the total density was held constant at 1.2 x 10(17) cm(-3). At 300 K the observations were consistent with singlet methylene ((1)CH(2)) and water as the main product channel with a small contribution of methanol. In contrast, at about 610 K three channels-formaldehyde isomers and methanol in addition to (1)CH(2) + H(2)O-are formed with similar yields. When acetone-d(6) was used, the production of both CHDO and CD(2)O was observed, indicating that two different formaldehyde-producing channels are operating simultaneously. These experimental results are compared with RRKM and master equation calculations on the basis of the properties of the methanol potential energy surface from a recent ab initio study.