Influence of Collision Energy on the Nascent OH(X2Π, v‘ ‘ = 0−4) Product Energetics for the Reaction of O(1D) with Ethane. A Laser-Induced Fluorescence and Quasiclassical Trajectory Study

Abstract

The full characterization of the nascent OH(X2Π, v‘ ‘, N‘ ‘, J‘ ‘, Λ‘ ‘) state distributions for the O(1D) + C2H6 → OH + C2H5 reaction has been experimentally performed using the laser-induced fluorescence technique to probe the v‘ ‘ = 0−4 levels of the OH molecules. This thorough study has been carried out for the first time using the N2O photodissociation at 193 nm to generate the O(1D) atoms (the average collision energy, 〈ET〉, is equal to 0.52 eV). By comparison with the experimental available data for 〈ET〉 = 0.27 eV (Park and Wiesenfeld, J. Chem. Phys. 1991, 95, 8166), it has been observed the existence of a small influence of ET on the dynamics of the title reaction, as only a somewhat higher rovibrational excitation of the OH product has been found on increasing the collision energy of the system. This supports the belief that the studied reaction essentially evolves through the insertion of the O(1D) atom into a C−H bond, yielding both short-lived (insertion/fast elimination microscopic mechanism) and long-lived (insertion/slow elimination microscopic mechanism) alcohol-type collision complexes. However, although not fully conclusive, some evidence has been found about the coexistence of a third reaction mode (abstraction), which may contribute to the formation of the highest vibrationally excited OH molecules with low rotational excitation. The dynamics of the insertion/fast elimination mechanism has been qualitatively reproduced using the quasiclassical trajectory method applied on two ab initio based analytical triatomic potential energy surfaces developed by us very recently for the related O(1D) + CH4 reaction, but with a mass correction.