Quantum Dynamics of H₂ and H₂O Dissociation on Cu(111) Surface

Mondal, Arobendo (2013) Quantum Dynamics of H₂ and H₂O Dissociation on Cu(111) Surface. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS Dissertation of Arobendo Mondal (08MS22)) Arobendo_Mondal-08MS22-MSThesis.pdf - Submitted Version Restricted to Repository staff only Download (4MB)

Abstract

In the field of Heterogeneous catalysis, the dissociative adsorption of molecules on metal surfaces has its own importance because of huge applications in industries. Production of most synthetic compounds involves reaction of molecules with metal surfaces. It is a fundamental step in corrosion and hydrogen storage in metal clusters and can be the rate limiting step of an overall reaction in the field of heterogeneous catalysis (for instance the dissociation of N₂ in the production of NH₃). Heterogeneous catalysis has attracted Nobel prizes for Fritz Haber, Carl Bosch, Irving Langmuir and Gerhard Ertl. My complete thesis has two parts, first in which I have studied the interaction of water molecule with the Cu(111) surface considering three degrees of freedom of water molecule and the second is effect of temperature on interaction of hydrogen molecule with Cu(111). Section I. Water dissociation on Cu (111): Effects of molecular orientation, rotation, and vibration on reactivity. Three dimensional time-dependent quantum mechanical method has been used to study the influence of orientation, rotation and vibration on the dissociation of water molecule on Cu(111), using London– Eyring–Polanyi–Sato (LEPS) potential energy surface (PES). Our calculations show that dependency of dissociation probability on the initial orientation of the molecule changes with the vibrational state of the molecule. It has also been found that for v₀ = 0 and 1, where n0 stands for the vibrational state of the pseudo diatomic HO-H, the rotational excitation of the molecule increases the reactivity, whereas for v₀ = 2, the rotational excitation of the molecule decreases the reactivity. Vibrational excitation of the molecule greatly enhances the dissociation probability. Section II. Lattice expansion effect on reactive scattering of H₂ from Cu(111). We have studied the effect of lattice expansion on the reaction of H₂ and D₂ on Cu(111) using quantum and quasi-classical dynamics. The specific reaction parameter (SRP) approach to density functional theory (DFT) has been used to compute the six-dimensional potential energy surface. Computed reaction probabilities and rotational quadrupole alignment parameters have been compared for surface temperatures Ts = 0 K and Ts = 925 K. Thermal expansion of the lattice has a considerable effect on barrier height, reaction probability as well as on the rotational quadrupole alignment parameter. The high symmetry sites of the Cu(111) surface for the expanded lattice show lower barrier heights compared to the 0 K lattice. Compared to the 0 K lattice, including the effect of surface temperature increases the reaction probability and decreases the rotational quadrupole alignment parameter for the same incident energy. Results for the expanded lattice are in better agreement with experimental data.

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