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 Title: MULTI-FACETED SPECTROSCOPIC STUDY OF THE STRUCTURAL CHANGES ASSOCIATED WITH ELECTRONIC EXCITATION OF METHYL ANTHRANILATE Author(s): Blodgett, Karl N. Contributor(s): Zwier, Timothy S.; Sibert, Edwin ; Fischer, Joshua L.; Sun, Dewei Subject(s): Vibrational structure/frequencies Abstract: Methyl anthranilate (MA) is the methyl ester of anthranilic acid. We present the jet-cooled Laser Induced Fluorescence (LIF) UV excitation spectrum, ground (S$_{0}$) and excited state (S$_{1}$) Fluorescence Dip Infrared (FDIR) spectra, IR-UV Holeburning (IR-UV HB) spectra, and Dispersed Fluorescence (DFL) spectra of the MA monomer and MA-H$_{2}$O complex. MA is a close analog of salicylic acid, a well-studied molecule thought to undergo keto-enol tautomerism involving excited state H-atom transfer. In the MA monomer, the C6 ring formed by the H$_{a}$NH$_{b}$ $^{...}$ O=C hydrogen bond in the ground state undergoes an unusual increase in hydrogen bond strength following electronic excitation to the S$_{1}$ state. This is evident in the spectroscopy in several ways. The LIF excitation and DFL spectra both show long progressions in several modes involving motion of the NH$_{2}$ and COOMe groups relative to one another. Furthermore, the coupled NH$_{2}$ symmetric and asymmetric stretch fundamentals appear to uncouple upon UV excitation, giving rise to a broadened (8 cm$^{-1}$ FWHM), nominally “free” N-H$_{a}$ stretch at 3458 cm$^{-1}$ and an N-H$_{b}$ stretch shifted all the way down to \~{}2900 cm$^{-1}$. FDIR spectra collected in the mid-IR frequency range show the change in hydrogen bond strength from the perspective of the C=O acceptor group, where the stretch fundamental is shifted down from its S$_{0}$ position at 1721 cm$^{-1}$ to 1637 cm$^{-1}$ in S$_{1}$. Calculations at the B3LYP-D3/def2TZVP level of theory in large measure capture these frequency shifts and give insight into likely explanations for such drastic changes. Similar behavior is observed in the MA-H$_{2}$O complex, although the extent of the hydrogen bond strengthening in the S$_{1}$ state is modulated by the HOH interactions with both the NH$_{2}$ and C=O groups. Issue Date: 2019-06-17 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/104338 DOI: 10.15278/isms.2019.ML07 Rights Information: Copyright 2019 Karl N. Blodgett Date Available in IDEALS: 2019-07-152020-01-25
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