Dynamics of reactions O (D1) + C₆H₆ and C ₆D₆

The reaction between O (D1) and C₆H₆ (or C ₆D₆) 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+ C5 H5 +H; the channels for formation of C5 H6 +CO and C6 H5 O+H from O (D1) + C₆H₆ and OD+ C6 D5 from O (D1) + C₆D₆ 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 (16) and OH (13) were recorded with a step-scan Fourier-transform spectrometer. At the earliest applicable period (0-5 μs), CO shows a rotational distribution corresponding to a temperature of ∼1480 K for =1 and 920-700 K for =2-6, indicating possible involvement of two reaction channels; the vibrational distribution of CO corresponds to a temperature of ∼5800 K. OH shows a rotational distribution corresponding to a temperature of ∼650 K for =1-3 and a vibrational temperature of ∼4830 K. The branching ratio of [CO] / [OH] =2.1±0.4 for O (D1) + C₆H₆ and [CO] / [OD] >2.9 for O (D1) + C₆D₆ 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 (D1) + C₆H₆ reaction. The experimentally observed branching ratios and deuterium isotope effect are consistent with those predicted from calculations.