RUI: Electronic Spectroscopy of Gold and Silver Monosulfides and Other Transition Metal-Containing Free Radicals

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In this project funded by the Chemical Structure, Dynamics, and Mechanisms A Program of the Division of Chemistry, Professor Thomas D. Varberg and his undergraduate student researchers at Macalester College are using visible and near-infrared spectroscopy to study the structure and bonding of gaseous molecules that contain a transition metal atom. One molecule under study is diatomic gold sulfide (AuS), which serves as a model for gold-sulfur bonding in more complex systems central to nanoscience and molecular self-assembly. The analysis of the experimental spectra are aided by complementary computer calculations on the targeted molecules are carried out in collaboration with Professor Keith Kuwata and his students. Transition metal chemistry and bonding is important to other areas of modern science, such as chemical catalysis, organometallic chemistry, nanoscience, and astronomy. Research on metal-containing diatomic molecules can serve as a useful model for bonding in more complicated systems.The project focuses on the molecules gold sulfide, silver sulfide, tantalum hydride and tantalum oxide. Electronic spectra in the visible and near-infrared are recorded with a high-resolution continuous-wave laser capable of resolving the vibrational, rotational and hyperfine structures. Analysis of the spectra leads to a detailed characterization of the electronic states and the chemical bonding, as well as providing accurate transition frequencies useful to other scientists. The supporting computational work utilizes equation-of-motion coupled-cluster methodology and provides accurate estimates of state energies, bond lengths and vibrational frequencies. A substantial broader impact of this work is to prepare Macalester students for graduate work in physical chemistry and chemical physics, including students from underrepresented groups. Furthermore, the targeted molecules exhibit simplified metal bonding that is relevant to more complex nanoparticle structures and to transition-metal catalysis of organic reactions.