PNNL

Abstract

Fourier transform infrared absorption spectra containing evidence for about two dozen spectral tunneling doublets are reported for gaseous tropolone(OH), tropolone(OD), and 18O,18O-tropolone(OH) in the 800 to 300 cm-1 spectral range. No FTIR absorption was detected in the 300-150 cm-1 range. The known zero-point (ZP) tunneling splitting values ?0 = 0.974 cm-1 for tropolone(OH) (Tanaka et al.) and 0.051 cm-1 for tropolone(OD) (Keske et al.) allow vibrational state-specific tunneling splittings ?v to be estimated for fundamentals including three with strong O•••O stretching displacements [cf. for tropolone(OH) ?13(a1) = 435.22 cm-1 with ?13 = 1.71 cm-1 = 1.76 ?0, and for tropolone(OD) ?13(a1) = 429.65 cm-1 with ?13 = 0.32 cm-1 = 6.3 ?0]. The majority of ?v splittings in the sub-800 cm-1 range are dilated relative to the isotopomer ?0 values. The FTIR spectra demonstrate the presence of dynamic couplings and potential function anharmonicity in addition to revealing ?v splittings and many 2 OH/D and 18O/16O isotope effects. Approximate values for the ZP splittings 88?0 and 86?0 of the doubly and singly 18O-labelled isotopomers of tropolone(OH) are obtained. The diverse values of the observed ?v/?0 splitting ratios underscore the inherent multidimensionality and the quantum corner-cutting activities entering the state-specific tunneling processes of the tropolone tautomerization reaction.