Title page for ETD etd-12012005-173625

Type of Document Dissertation
Author Day, Brian Scott
URN etd-12012005-173625
Title The Dynamics of Gas-Surface Energy Transfer in Collisions of Rare Gases with Organic Thin Films
Degree PhD
Department Chemistry
Advisory Committee
Advisor Name Title
Morris, John R. Committee Chair
Anderson, Mark R. Committee Member
Crawford, Daniel T. Committee Member
Deck, Paul A. Committee Member
Tissue, Brian M. Committee Member
  • Ultra-high vacuum
  • Molecular beam
  • Self-assembled monolayers
Date of Defense 2005-07-18
Availability unrestricted
Understanding mechanisms at the molecular level is essential for interpreting and

predicting the outcome of processes in all fields of chemistry. Insight into gas-surface

reaction dynamics can be gained through molecular beam scattering experiments

combined with classical trajectory simulations. In particular, energy exchange and

thermal accommodation in the initial collision, the first step in most chemical reactions,

can be probed with these experimental and computational tools.

There are many questions regarding the dynamic details that occur during the

interaction time between gas molecules and organic surfaces. For example, how does

interfacial structure and density affect energy transfer? What roles do intramonolayer

forces and chemical identity play in the dynamics? We have approached these questions

by scattering high-energy, rare gas atoms from functionalized self-assembled

monolayers. We used classical trajectory simulations to investigate the atomic-level

details of the scattering dynamics. We find that approximately six to ten carbon atoms

are involved in impulsive collision events, which is dependent on the packing density of

the alkyl chains. Moreover, the higher the packing density of the alkyl chains, the less

energy is transferred to the surface on average and the less often the incident atoms come

into thermal equilibrium with the surface. In addition to the purely hydrocarbon

monolayers, organic surfaces with lateral hydrogen-bonding networks create more rigid

collision partners than surfaces with smaller inter-chain forces, such as van der Waals

forces. Finally, we find some interesting properties for organic surfaces that possess

fluorinated groups. For argon scattering, energy transfer decreases with an increasing

amount of surface fluorination, whereas krypton and xenon scattering transfer most

energy to monolayers terminated in CF3 groups, followed by purely hydrocarbon

surfaces, and then perfluorinated surfaces.

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