High-resolution studies of tropolone in the S0 and S1 electronic states:: Isotope driven dynamics in the zero-point energy levels -: art. no. 074309

Rotationally resolved microwave (MW) and ultraviolet (UV) spectra of jet-cooled tropolone have been obtained in S-0 and S-1 electronic states using Fourier-transform microwave and UV-laser/molecular-beam spectrometers. In the ground electronic state, the MW spectra of all heavy-atom isotopomers including one O-18 and four C-13 isotopomers were observed in natural abundance. The OD isotopomer was obtained from isotopically enriched samples. The two lowest tunneling states of each isotopomer except O-18 have been assigned. The observed inversion splitting for the OD isotopomer is 1523.227(5) MHz. For the asymmetric C-13 structures, the magnitudes of tunneling-rotation interactions are found to diminish with decreasing distance between the heavy atom and the tunneling proton. In the limit of closest approach, the 0(+) state of O-18 was well fitted to an asymmetric rotor Hamiltonian, reflecting significant changes in the tautomerization dynamics. Comparisons of the substituted atom coordinates with theoretical predictions at the MP2/aug-cc-pVTZ level of theory suggest the localized 0(+) and 0(-) wave functions of the heavier isotopes favor the C-OH and C=O forms of tropolone, respectively. The only exception occurs for the C-13-OH and C-13=O structures which correlate to the 0(-) and 0(+) states, respectively. These preferences reflect kinetic isotope effects as quantitatively verified by the calculated zero-point energy differences between members of the asymmetric atom pairs. From rotationally resolved data of the 0(+)<- 0(+) and 0(-)<- 0(-) bands in S-1, line-shape fits have yielded Lorentzian linewidths that differ by 12.2(16) MHz over the 19.88(4) cm(-1) interval in S-1. The fluorescence decay rates together with previously reported quantum yield data give nonradiative decay rates of 7.7(5)x10(8) and 8.5(5)x10(8) s(-1) for the 0(+) and 0(-) levels of the S-1 state of tropolone. (c) 2006 American Institute of Physics.