Theoretical and Experimental Investigation of the Dynamics of the Production of CO from the CH3 + O and CD3 + O Reactions

Abstract

Combined experimental and theoretical investigations of the title reactions are presented. Time-resolved Fourier transform infrared (FTIR) emission studies of CO (v = 1) produced from the CH{sub 3} + O and CD{sub 3} + O reactions show that there is approximately a one-third reduction in the branching to the CO channel upon deuteration of the methyl radical. Direct dynamics, classical trajectory calculations using a B3LYP potential surface, confirm the existence of the CO producing channel. The calculations show that the CO comes from the decomposition of HCO produced by the elimination of H{sub 2} from highly vibrationally excited methoxy radicals. Scans of the potential surface reveal no saddle point for the direct elimination of H{sub 2} from methoxy. The minimum-energy path for this elimination is a stepwise process involving first a CH bond cleavage, forming H + H{sub 2}CO, followed by an abstraction, forming H{sub 2} + HCO. However, at the high internal energies produced in the initial O + CH{sub 3} addition, trajectories for the direct elimination of H{sub 2} from methoxy are observed. The predicted branching ratio between the CO and H{sub 2}CO channels is in good agreement with previous room-temperature measurements, and there is predicted to bemore » little temperature dependence to it. The observed reduction in the branching to the CO channel upon deuteration is also well reproduced in the calculations.« less