Atomic-level Imaging and Molecular Beam Scattering Studies of Interfacial Chemical Dynamics

University Of Chicago, Chicago IL

Investigators

Abstract

With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) program in the Division of Chemistry, Professor Steven Sibener of the University of Chicago is studying chemical reactions that occur when molecules collide with surfaces. Understanding these gas-surface reactions is challenging, since the likelihood of reaction depends on the speed and angle that molecules strike the surface, and these are difficult to control. Further complicating matters, when surfaces are viewed up close, they exhibit many atomic-scale structures, including steps, missing atoms, and islands, each of which can exhibit different reactivity. Professor Sibener and his students will use molecular beams to control the collision with the surface and then visualize how molecules attach to, react, and depart from the interface. Their discoveries could reveal the underlying mechanisms that govern chemical reactivity in a host of emerging technologies, including the design and development of new functional materials for sustainable chemistry and quantum information science applications. The project will also contribute to the development of the Nation's science, technology, engineering, and mathematics (STEM) workforce by providing research opportunities for undergraduate students, graduate students, and postdoctoral scholars, as well as outreach activities involving local schools and Chicago’s Museum of Science and Industry. This project will examine issues in surface chemical dynamics that include site specific reactivity, adiabatic and non-adiabatic gas-surface interactions such as dissociative chemisorption including energy dissipation and surface mobility, directionally-controlled deposition and film growth, thin film reactivity, and geometry-constrained and stereo-specific reaction studies in which energetic atomic species react with molecules that are pre-aligned due to the nature of their bonding and film structure. Reactants will be pre-aligned using either oriented surface adsorption or pre-ordered reactive end-groups on self-assembled monolayers, thus presenting sterically controlled reaction partners to incident gas phase reagents. This will allow systematic exploration of molecular reactivity and reaction pathways using defined entrance channel reaction conditions including well-defined energy and polar/azimuthal angles of attack with respect to the molecular framework. Comparisons with dissociative chemisorption and reactive scattering calculations, done in conjunction with quantum theory and molecular dynamics simulations, will lead to precision tests of calculated reaction potential energy surfaces and mechanistic reaction pathways. Control of reagent energy, incident angle, intensity, and quantum state will enable the examination of interfacial chemistry under non-equilibrium energetic conditions. 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.