Chemical Dynamics of Polyatomic Molecules at Surfaces: New Insights into Complex Systems from State-Selected Studies

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In this project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Arthur Utz from Tufts University is using sophisticated laser and molecular beam techniques to study the reactions of molecules on metal surfaces. Metal particles are commonly used as catalysts in commercial chemical processes. They selectively convert reactants to the desired product, reduce production of wasteful byproducts, increase reaction rate, and lower energy requirements. Understanding how catalysts work is a key step toward improving their performance. The problem is challenging, however, due to the wide range of reactant energies, and the many different atomic structures found on a working catalyst. To unravel this complexity, Professor Utz and his students are preparing reactants with precise quantities of energy. They then measure their reactivity on a series of surfaces containing well-defined structures that resemble the features present on a working catalyst. The work is providing a systematic and quantitative understanding of how reactant energy, and surface structure, lead to catalytic activity. Insights gained from the project could advance our ability to design and optimize catalysts, which could have important benefits to society. The project is also training students in advanced experimental methods and interfacial science, and it is providing outreach activities that stimulate interest, and enrich the K-12 Science and Technology curriculum at local schools. The project focuses on the energetics and dynamics of dissociative chemisorption to build a mechanistic picture of catalytic activity. A key goal is to understand how increasing the structural and chemical complexity of the gas phase reagent and the surface affects reactivity. A supersonic molecular beam and infrared laser, respectively, impart reactant molecules with a precisely defined kinetic and internal energy. Metal surfaces are chosen to systematically introduce structural features characteristic of working catalysts. Molecular beam reflectivity and surface-sensitive spectroscopies quantify reaction probability as a function of reagent's translational, vibrational, and rotational energies, as well as the surface structure and temperature. In concert with collaborators' electronic structure and reactive scattering calculations, the results paint a detailed picture of the underlying processes that govern gas-surface reactivity and reveal how reactivity patterns persist or change as complexity increases.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.