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Abstract

The study of gas-surface interaction reactivity and dynamics is important both for the fundamental knowledge and to aid the development of various applications. Thorough understanding of interactions of gases with ice and organic films can help answer important questions related to geophysics and global energy issues. Additionally, experimental measurements of these processes can be used to validate advanced computer models. The experiments in this thesis have been carried out under well-defined condition, namely in ultrahigh vacuum and using highly-ordered surfaces and molecular beams. The Thesis is mainly focus on two kinds of interactions: atomic oxygen with organic thin films, and gaseous species with ice surface. The first aspect investigated kinetics and dynamics of bimolecular reactions utilizing supersonic beams of atomic oxygen and self-assembled monolayers (SAMs). With combination of in situ infrared spectroscopy and scanning tunneling microscopy, the mechanism of the reaction of O(3P) with phenyl-substituted alkynes has been characterized and confirmed. This technique is potential to elucidate orientation-dependent kinetics, with the added ability to “collisionally stabilize” reactive intermediates. Here, we demonstrated a new mechanism of energetic ballistic deposition, to trap and concentrate gases into ice at a surface temperature where gases adsorption is infeasible. The embedding of CO2, CF4 and other small atoms and molecules into ice has been characterized. The results show that ice composition can be modified by gas with high translational energies. These findings have implications for many fields including environmental science, chemical composition of astrophysical icy bodies in space. This thesis also includes a finding of reverse water-gas shift (RWGS) reaction in our supersonic nozzle with catalytic metal surface. Utilizing a supersonic expansion beam technique,we demonstrate highly selective reactivity between carbon dioxide and molecular hydrogen involved in the RWGS reaction. This reaction exhibits reaction yields as high as 90% at nozzle temperatures approaching 750 °C. The metal surface was found to serve as a heterogeneous catalyst for the reaction. This supersonic expansion technique provides opportunities to screen various catalytic reactions under high temperature and high pressure conditions. Thus, it is feasible for this technique to facilitate such reactions with surface-generated gas-phase radicals, followed by rapid desorption and cooling of the intermediate products.

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