PNNL

Abstract

The Fourier transform infrared spectrum of tropolone(OH) vapor in the 1175-1700 cm-1 region is reported at 0.0025 and 0.10 cm-1 spectral resolutions. The 12 vibrational fundamentals in this region of rapidly rising vibrational state density are dominated by mixtures of the CC, CO, CCH, and COH internal coordinates. Estimates based on the measurement of sharp Q branch peaks are reported for 11 of the spectral doublet component separations DSv =|?v ± ?0|, ?0 = 0.974 cm-1 is the known zero-point splitting, and three a1 modes show tunneling splittings ?v ˜ ?0, four b2 modes show splittings ?v ˜ 0.90?0, and the remaining four modes show splittings ?v falling 5-14% from ?0. Significantly, the splitting for the nominal COH bending mode v8 (a1) is small, that is, 10% from ?0. Many of the vibrational excited states demonstrate strong anharmonic behavior, but there are only mild perturbations on the tautomerization mechanism driving ?0. The data suggests, especially for the higher frequency a1 fundamentals, the onset of selective intramolecular vibrational energy redistribution processes that are fast on the time scale of the tautomerization process. These appear to delocalize and smooth out the topographical modifications of the zero-point potential energy surface that are anticipated to follow absorption of the vv photon. Further, the spectra show the propensity for the ?v splittings of b2 and other complex vibrations to be damped relative to ?0.