Visualizing Ultrafast Chemical Reaction Dynamics

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With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) program in the Division of Chemistry, Professors Roseanne Sension and James Penner-Hahn of the University of Michigan are combining advanced visible and x-ray laser methods to watch the movement of atoms and electrons during the making and breaking of chemical bonds. Chemical reactions are controlled by the coupled motions of atoms and electrons on time scales measured in trillionths of a second or shorter. No ordinary camera can capture this movement. Professors Sension and Penner-Hahn and their students will use very short x-ray pulses to image the coupled motions of atoms and electrons in photochemical reactions, focusing on one element at a time. Their discoveries could lead to the design of more efficient chemicals used in applications ranging from photo-selective drug delivery to industrially important photocatalysts. This project will also contribute to education and human resource development by training a diverse group of graduate and undergraduate students to work at the interface of x-ray physics, optics, chemical dynamics, and inorganic chemistry. Chemical reactions involve changes in atomic arrangement, electron distribution, and bonding. Professors Sension and Penner-Hahn combine strengths in ultrafast spectroscopy and x-ray spectroscopy to visualize, describe, and control these dynamics. By using light to initiate reactions, the molecular behavior can be synchronized, allowing studies on time scales ranging from attoseconds, for electronic rearrangements, to femtoseconds and picoseconds for atomic motion. Polarization and time-resolved x-ray spectroscopies will provide an element specific view of chemical reaction dynamics, complementing and extending the view provided by optical and vibrational spectroscopies. The results could challenge conventional thinking, identify new phenomena, and overturn previous models. In this project Professors Sension and Penner-Hahn and their students will focus on the ultrafast coherent dynamics of transition metal containing systems, including organocobalt complexes, that drive both biologically relevant transformations and technologically important molecular conversions, as well as the light-driven conformational changes in polyenes that underlie processes ranging from vision to molecular motors. Ultrafast x-ray spectroscopies are applicable to a broad range of systems active in transport, energy harvesting, energy storage and biological systems. The broader impacts of this work include the development of methods that enable a wider use of time-resolved x-ray spectroscopies in the chemical community.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.