Dynamics of reactions O((1)D)+C(6)H(6) and C(6)D(6)

Abstract

The reaction between O((1)D) and C(6)H(6) (or C(6)D(6)) was investigated with crossed-molecular-beam reactive scattering and time-resolved Fourier-transform infrared spectroscopy. From the crossed-molecular-beam experiments, four product channels were identified. The major channel is the formation of three fragments CO+C(5)H(5)+H; the channels for formation of C(5)H(6)+CO and C(6)H(5)O+H from O((1)D)+C(6)H(6) and OD+C(6)D(5) from O((1)D)+C(6)D(6) are minor. The angular distributions for the formation of CO and H indicate a mechanism involving a long-lived collision complex. Rotationally resolved infrared emission spectra of CO (1 <=upsilon <= 6) and OH (1 <=upsilon <= 3) were recorded with a step-scan Fourier-transform spectrometer. At the earliest applicable period (0-5 mu s), CO shows a rotational distribution corresponding to a temperature of similar to 1480 K for upsilon=1 and 920-700 K for upsilon=2-6, indicating possible involvement of two reaction channels; the vibrational distribution of CO corresponds to a temperature of similar to 5800 K. OH shows a rotational distribution corresponding to a temperature of similar to 650 K for upsilon=1-3 and a vibrational temperature of similar to 4830 K. The branching ratio of [CO]/[OH]=2.1 +/- 0.4 for O((1)D)+C(6)H(6) and [CO]/[OD]>2.9 for O((1)D)+C(6)D(6) is consistent with the expectation for an abstraction reaction. The mechanism of the reaction may be understood from considering the energetics of the intermediate species and transition states calculated at the G2M(CC5) level of theory for the O((1)D)+C(6)H(6) reaction. The experimentally observed branching ratios and deuterium isotope effect are consistent with those predicted from calculations.