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Open Access Dissertation
Doctor of Philosophy (PhD)
Year Degree Awarded
Month Degree Awarded
The adsorption and dissociation of small molecules on metal surfaces are key steps in many industrial reactions. A detailed understanding of the dynamics of these reactions provides us with the ability to control the outcome and efficacy of the reactions. The molecule-metal interactions will lead to reorientation, energy redistribution, or bond dissociation in the molecule. The process is strongly depending upon the initial conditions, i. e. the incident energy and vibrational state of the molecule, and the surface temperature. We use a fully quantum approach to compute the dissociative sticking probability of the molecules at zero overage, on the surface of metal catalysts. We use density functional theory (DFT) based electronic structure calculations to construct a reaction path Hamiltonian (RPH) for reaction. Using well tested sudden methods for adding the effects of lattice motion into quantum reactive scattering calculations allows us to directly compare the results from our theory with molecular beam studies.
Using these methods, we have explored the dissociative chemisorption of H2O, HOD, and D2O on Ni(111), and found that for this late barrier system, excitations in bending and stretching vibrational modes enhance the dissociative sticking. The motion of the lattice atoms near the dissociating molecule was found to modify the height of the barrier, leading to a strong variation in reactivity with surface temperature.
We also studied the dissociative chemisorption of CO2 on Ni(100) and the Ni(711) stepped surface. The mechanism for dissociation is similar on the two surfaces, including the formation of a bent anionic chemisorption precursor state. Vibrational excitation of the incident CO2 molecule can enhance the reactivity for low incident energies, and the biggest efficacy corresponds to the bending mode that leads the molecule to the bent precursor state.
The vibrationally inelastic scattering of methane molecules from a Ni(111) at low incident energies was studied and we found that the vibrational energy initially in one vibrational state, can distribute into other states upon collision. We have computed this energy distribution using SRP density functional which is a van der Walls correlation functional. At low incident energies the results are similar for PBE and SRP.
Farjamnia, Azar, "Gas-Surface Interactions: Reactive and Non-Reactive Scattering" (2018). Doctoral Dissertations. 1236.