RUI: Spectroscopic and Computational Studies of Cyclic Enone Molecules in Electronic Excited States

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In this project funded by the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A), Professor Stephen Drucker of the University of Wisconsin-Eau Claire (UW-Eau Claire) is investigating how chemical reactions are affected by ultraviolet (UV) light. Chemical reactions started by exposure to light are called photochemical reactions. These reactions can contribute to environmental problems. On the other hand, they can also be beneficial when carried out under carefully controlled conditions. For instance, photochemical reactions can be used to make new materials that would benefit society. In the future, the most detailed information about the steps taken when photochemical reactions occur may come from computer modeling. Computational scientists can predict the structures of molecules produced during photochemical reactions, but the computational methods do not always yield accurate results and thus, they are still being improved. Professor Drucker’s research uses laser spectroscopy to test computational predictions on molecules that can take part in photochemical reactions. Undergraduate student researchers perform the experimental work. UW-Eau Claire undergraduates gain experience with lasers, electronics, computational chemistry and experiment design. This research project helps prepare them for graduate programs and STEM-based careers. In this project, students are recording vibronically resolved spectra of singlet-triplet transitions in gas-phase monocyclic enone molecules. Molecules under investigation are 2-cyclopenten-1-one (2CPO), 2-cyclohexen-1-one (2CHO), and 4H-pyran-4-one (4PN). The objective is to determine fundamental frequencies for vibrational modes in the lowest triplet excited states of the test molecules. The project focuses on triplet-state vibrations in the C=O/C=C stretch region of the spectra. Experimentally determined fundamentals for these stretching modes augment frequency information previously obtained for ring vibrational modes and carbonyl wagging modes. Those bands appear in the lower-energy region of each spectrum near the origin band of the S0-T1 transition. In previous work, the research group used cavity ringdown (CRD) spectroscopy at room temperature to measure the lower-frequency fundamentals. However, in the higher-frequency C=O stretch region, the S0-T1 CRD bands at room temperature tend to be submerged by vibronic hot bands belonging to the S0-S1 transition. To eliminate this interference, the S0-T1 spectra in this project are recorded under jet-cooled conditions, using two-color resonant enhanced two-photon ionization to detect the transitions. Experimentally determined excited-state fundamental frequencies are compared to predictions from a variety of state-of-the art computational methods. Broader impacts of the research promote academic and intellectual growth of undergraduate students. These educational activities include scientific training, enhancement of the academic curriculum at UW-Eau Claire through the development of a computational chemistry course, and the expansion of access to contemporary physical chemistry research by groups underrepresented in STEM.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.