Quantum State Resolved Studies of Gas-Surface Interaction Dynamics

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In this project in the PhysicalChemistry program of the Chemistry Division, Professor Greg O. Sitz of the Chemistry Department of the University of Texas at Austin will perform a series of gas-surface scattering experiments. A combination of molecular beam and laser based state preparation and detection techniques will be used to performm fully quantum state resolved studies of gas-surface interaction dynamics. The scattering and dissociation of molecular hydrogen and deuterium from single crystal copper surfaces will be studied to determine the relative importance of translational, rotational, vibrational and molecular alignment in dermining the outcome of the scattering event. Stimulated Raman scattering will be used to prepare hydrogen molecules incident on the copper surface in a selected rotational state of the first excited vibrational state. Scattered molecules will be detected in a quantum state specific manner by multiphoton ionization. The initial encounter of a molecule with a solid surface can lead to several possible results depending on the molecule , the surface, and the energy partitioning amongst the many available degrees of freedom. These possibilities include inelastic scattering, trapping, sticking and bond breaking. In the last case, a bond in the molecule can be broken, paying the energy price by forming one or more chemical bonds to the surface. This is the essence of the ability of many surfaces to promote or participate in chemical reactions. In many cases of interest, however, even though the reaction is energetically favorable, the reaction probability is low because of the presence of a barrier: the reaction is said to be activated. Of central concern is the nature of this activation barrier and the dynamical mechanism for crossing it. This research focuses on gas-surface interactions in systems where dissociative adsorption is an activated process. By performing this research with fully state resolved measurements new insight into surface dynamics will be gained and existing theories will be stringently tested.