A Combined Quantum Chemistry and RRKM Calculation Predicts the O(1D) + C2H6 Reaction Can Produce Water Molecule in a Collision-Free Crossed Molecular Beam Environment

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

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<or=upsilon<or=6) and OH (1<or=upsilon<or=3) were recorded with a step-scan Fourier-transform spectrometer. At the earliest applicable period (0-5 mus), CO shows a rotational distribution corresponding to a temperature of approximately 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 approximately 5800 K. OH shows a rotational distribution corresponding to a temperature of approximately 650 K for upsilon=1-3 and a vibrational temperature of approximately 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.

Multiple channel dynamics in the O(1D) reaction with alkanes

In this article, we briefly review the recent experimental studies of the multiple channel dynamics of the O((1)D) reaction with alkane molecules using the significantly improved universal crossed molecular beam technique. In these reactions, the dominant reaction mechanism is found to be an O atom insertion into the C-H bond, while a direct abstraction mechanism is also present in the OH formation channel. While the reaction mechanism is similar for all of these reactions, the product channels are quite different because of the significantly different energetics of these reaction channels. In the O((1)D) reaction with methane, OH formation is the dominant process while H atom formation is also a significant process. In the O((1)D) reaction with ethane, however, the CH(3) + CH(2)OH is the most important process, OH formation is still significant and H atom formation is of minor importance. A new type of O atom insertion mechanism (insertion into a C-C bond) is also inferred from the O((1)D) reaction with cyclopropane. Through these comprehensive studies, complete dynamical pictures of many multiple channel chemical reactions could be obtained. Such detailed studies could provide a unique bridge between dynamics and kinetics research.