Comptational and theoretical study of energy transfer and chemical reaction in collisions of rare gas and oxygen atoms with hydrocarbon molecules and surfaces

We have developed a model for rare gas atoms scattering off hydrocarbon surfaces and used this model in a classical dynamics computer simulation of the energy transfer dynamics for rare-gas atoms scattering off an alkyl thiolate self-assembled monolayer (SAM) surface. The simulation gives near quantitative agreement with experiments of the Sibener Research Group, and can be used to simulate and interpret experiments of rare gas/alkyl thiolate SAM scattering. The simulations show that thermal desorption is not necessarily required to have a Boltzmann component in the final energy distribution of the scattered rare-gas atoms. We also developed and implemented a normal mode Hamiltonian to study mode specific energy transfer as well as intramolecular vibrational energy re-distribution (IVR) for Ne-SAM scattering. Simulations with this model show that there are two major types of energy transfer pathways in rare gas/SAM scattering, giving rise to a bimodal final translational energy distribution of the scattered rare gas atoms. A washboard with moment of inertia (WBMI) model was also developed, in collaboration with Dr. John C. Tully, to represent gas-surface scattering and implemented for Ne and Ar-atom scattering off a SAM surface.; We used high level of electronic structure theory methods to study a series of reactions (primary, secondary, and unimolecular dissociation) associated with O(3P) + C₂H₆ collisions. A semiempirical PM3-SRP potential energy model, with distance dependence scaling factors, was implemented to fit the high-level electronic structure calculations. A quasiclassical direct dynamics trajectory simulation was implemented, with PM3-SRP, to simulate 5 eV collisions between O(3P) and C ₂H₆. A variety of reaction pathways were identified. Collisions at this high energy mimics the collisions between O(3P) and the surface of space craft in low earth orbit (LEO).