Detailed experimental and theoretical investigations have been carried out for the reaction of O(3P) with CH3CH3 at collision energies in the range of 80-100 kcal mol-1. Experiments were performed on a crossed molecular beams apparatus with a laser breakdown source (which produces beams of O(3P) with average velocities of 6.5 to 8.5 km s-1) and a pulsed supersonic source of CH3CH3 having an average velocity of ∼0.8kms-1. A rotatable quadrupole mass spectrometer allowed universal detection, with angular and velocity resolution of products scattering from the crossing region of the two reagent beams. Theoretical calculations were carried out in two stages,electronic structure calculations to characterize the stationary points associated with the title reaction and (2) direct dynamics calculations employing the MSINDO semiempirical Hamiltonian and density functional theory (B3LYP/6-31G**). The dynamics of O-atom inelastic scattering and H-atom abstraction to form OH + C2H5 were clearly revealed by the experiment and were matched well by theory. Both of these processes favor high-impact parameters, with most of the available energy going into translation, indicating a stripping mechanism for H-atom abstraction. H-atom abstraction was the dominant reactive pathway, but H-atom elimination to form OC2H5 + H was also inferred from the experimental results and observed in the theoretical calculations. This reaction proceeds through small-impact-parameter collisions, and most of the available energy goes into internal excitation of the OC2H5 product, which likely leads to secondary dissociation to H2CO + CH3 or CH3CHO + H. A relative excitation function for the H-atom elimination channel was also measured and compared to a calculated absolute excitation function. The theoretical calculations also identified several additional reaction pathways with low relative yields, including C-C bond breakage to form OCH3 + CH3. Interference from OC2H5 decomposition products in the experiment inhibited the unambiguous observation of the low-yield reaction pathways that were identified by theory, although an upper limit for the relative yield of C-C bond breakage was determined.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry