State-to-State Photodissociation of Polyatomic Free Radicals: Nonadiabatic Dynamics and Quantum Coherence

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The Chemical Structure, Dynamics and Mechanisms A (CSDM-A) program of the Chemistry Division funds Professor Jingsong Zhang of the University of California at Riverside to investigate the photodissociation dynamics of polyatomic free radicals. Free radicals are important reactive intermediates in many chemical environments (such as combustion and atmospheric chemistry). This research aims to understand the photochemistry of polyatomic radicals and the roles of interacting electronic states with quantum accuracy. The knowledge (free radical electronic structures, energetics, reaction mechanisms, etc.) from this project is valuable to the combustion, atmospheric chemistry, theoretical chemistry, and physics communities. The project trains graduate students and prepares them for careers in academia or industry and promotes research experience of women and underrepresented minority undergraduate students. The project reaches out to the diverse student population in the Riverside and San Bernardino community colleges. This program also mentors economically disadvantaged high school students for summer research internships.The project focuses on the hydroxymethyl, hydroperoxy, and methylene radicals. Experimentally, the free radicals are produced by photolysis of suitable precursors and subsequent reactions and are cooled in a molecular beam with a well-defined initial energy. The free radicals are photodissociated under a single collision condition by tunable laser radiation, producing hydrogen atom photoproducts. The high-n Rydberg atom time-of-flight technique is utilized to measure state-resolved product kinetic energy and angular distributions. These distributions are closely related to theoretical calculations and are central to understanding photodissociation dynamics and mechanisms. The research generates high-quality data and benchmarks to test quantum mechanical theories of the excited open-shell species.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.