# HIGH RESOLUTION $S_{1} \leftarrow S_{0}$ FLUORESCENCE EXCITATION SPECTROCOPY OF THE TAUTOMERS OF 2-$HYDROXYPYRIDINE.^{1}$

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 Title: HIGH RESOLUTION $S_{1} \leftarrow S_{0}$ FLUORESCENCE EXCITATION SPECTROCOPY OF THE TAUTOMERS OF 2-$HYDROXYPYRIDINE.^{1}$ Creators: Held, A.; Plusquellic, D. F.; Pratt, D. W. Issue Date: 1990 Publisher: Ohio State University Abstract: Three separate $S_{1}-S_{0}$ electronic origins are known to exist for 2-hydroxypyridine $(2HP).^{2}$ The highest energy origin is thought to belong to the lactim (2-pyridinol) tautomeric form while the two lower energy origins are thought to belong to two different conformers of the lactam (2-pyridone) form. We have examined these two origins at high resolution using the molecular beam laser spectrometer and determined the inertial parameters of both the S0 and S1 zero-point vibrational levels (ZPL's) in both 2HP and hydroxy-deuterated 2HP (2DP). We also have performed geometry optimizations of both tautomers at the Hartree-Fock level using a 3-21G basis set. The rotational constants of the S0 ZPL's participating in the two lower energy origins in 2HP are the same within experimental error $(\pm 0.1 MHz)$, showing that both transitions originate in the same tautomeric (and conformeric) form. This form is shown to be the lactam form of 2HP by comparing the theoretical geometries and the measured rotational constants of $S_{0}$ 2HP and 2DP, which makes possible the determination of the COM coordinates of the isotopically substituted atom using Kraitchman's equations. Changes in these coordinates, revealed by applying the same strategy to the two $S_{1}$ ZPL's, show that electronic excitation produces two different non-planar equilibrium geometries of the lactam form of 2HP that have different energies. Thus, the two lower energy $0_{0}^{0}$ bands in 2HP originate in a single conformer but terminate in two different conformers of the lactam form of 2HP. A comparison of the measured inertial defects of the two S1 conformers provides considerable information about their structural differences. Similar experiments on the highest energy $0_{0}^{0}$ band of 2HP are in progress Description: $^{1}$ Work supported by NSF. $^{2}$ M. R. Nimlos, D. F. Kelley, and E. R. Bernstein, J. Phys. Chem. 93, 643 (1989). Author Institution: Department of Chemistry, University of Pittsburgh URI: http://hdl.handle.net/1811/18382 Other Identifiers: 1990-WH-1