Polarization Infrared Spectroscopy of Adsorbed Molecules on Cu(lll) and Pd/Cu Bimetallic Surfaces

Infrared (IR) spectroscopy is a common technique utilized primarily for the chemical identification of molecules via their vibrational frequencies. It is prominent in surface science due to its adaptability, applicability, and low-cost instrumentation. Polarization-dependent reflection absorption infrared spectroscopy (PD-RAIRS) can be used to study molecules adsorbed on surfaces in the presence of gas-phase reactants and products during surface-catalyzed reactions. In the first half of this thesis, two novel applications of PD-RAIRS are demonstrated. The first involves the isotherms' measurements for propyne's reversible adsorption on a well-characterized Cu(111) surface. In the second application, The ability of CO to restructure Cu(111) under ambient conditions is shown. This phenomenon is essential because of CO's multiple roles, including reactant, poison, product, or additive, in catalytic processes such as CO hydrogenation, CO oxidation, methanol synthesis, and the water gas shift reaction. In the second half of this thesis, some of the limitations of PD-RAIRS are discussed, and a more advanced version called polarization-modulated RAIRS is introduced. An approach is demonstrated to meet the ever-existing materials gap (describes the differences in complexity between single-crystal surfaces and commercial catalysts) and pressure gap (refers to the environment in which studies occur) between surface science and industrial catalysis studies. To bridge these gaps, we have constructed an improved dual ultrahigh vacuum chamber for conducting surface science studies from UHV to atmospheric pressure. A unique design of a vacuum box for optical elements is also described. Finally, towards the end of this thesis, IR polarization spectroscopy of adsorbed molecules related to selective hydrogenation reactions on Cu and Pd/Cu bimetallic surfaces is shown, demonstrating applications of the newly developed system.