Theoretical Studies of Spectral Signatures of Large Amplitude Vibrational Motions

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Anne McCoy of Ohio State University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry division to develop theoretical and computational tools needed to understand the spectra of molecules in which the atoms in the molecules undergo large amplitude motions. The work has a particular focus on protonated and hydrogen bonded systems. This class of molecules can be found close to home in our atmosphere and also far away in the interstellar medium. Such molecular systems also provide prototypes to understand the solvation of ions in water. Experimentalists use vibrational spectroscopy to study these molecules. In the case of astrochemistry, vibrational spectroscopy provides the best method for studying chemical composition. Unlike many common molecules, however, the bonding in these systems is weak. Most of the models that have been developed to predict and interpreted rotation/vibration spectroscopy do not apply to them. By developing these new approaches, McCoy and her research group are addressing this deficiency. The results of these studies will be used to develop connections between spectra and structure and bonding. McCoy and her research group collaborate with experimental research groups on all of these projects. This research program provides educational and research opportunities for both undergraduates and graduate students. McCoy is very active in encouraging women and other members of under-represented groups to pursue careers in science. Of particular interest is the interaction between rotation and vibration motions. To this end, the McCoy group is developing several Monte Carlo-based techniques to probe these interactions. Much of the proposed work involves the Diffusion Monte Carlo approach, with an emphasis on extending the range of properties that can be calculated using this general approach. In addition, they employ an approach based on Monte Carlo sampling of potential surfaces to deepen the understanding of the origins of the broadening of spectral features in hydrogen bonded systems. Specific applications include molecules, specifically H5+ and CH5+ that are of astrochemical interest, as well as several studies that probe the origins of spectral signatures of hydrogen bonding.