Theoretical Studies of the O(3P) + Ethane Reaction

The O( 3 P ) + C 2 H 6 reaction has been studied at two levels of theory. First, we have carried out high-level ab initio calculations of the various asymptotes and stationary points that are relevant to collision energies associated with low Earth orbit (LEO) conditions. CCSD(T)/cc-pVTZ calculations indicate that C−C breakage can occur with energies well below those encountered in LEO and that the barrier for this reaction is the lowest energy other than that for H abstraction to generate OH. Second, we have performed extensive direct dynamics calculations employing the MSINDO semiempirical Hamiltonian and density functional theory (B3LYP/6-31G*) at various collision energies relevant to LEO. OH abstraction is the dominant process at all energies, but other products are also important. Among these, H-atom elimination to give OC 2 H 5 + H is the most important, although other products such as H 2 O + C 2 H 4, OC 2 H 4 + 2H, and OCH 3 + CH 3 are also generated at high collision energies. Analysis of product energy distributions reveals the expected trends for H abstraction and H elimination, with the behavior for OCH 3 + CH 3 being closer to that for abstraction. Angular distributions for OH under LEO conditions show forward scattering, whereas those for H elimination and C−C breakage are sideways and backward peaked, respectively. Detailed analysis of the dynamical information will hopefully lead to a better understanding of the microscopic reaction mechanisms of the fundamental processes that contribute to LEO materials erosion.