The 370-nm electronic spectrum of tropolone: Evidence from single vibronic level fluorescence spectra regarding the assignment of some vibrational fundamentals in the [formula omitted] and [formula omitted] states

Abstract

Single vibronic level fluorescence (SVLF) spectra of tropolone from vibronic levels in the A ̃ 1B 2 electronic state, in combination with recently reported supersonic jet spectra, have enabled the assigning of many absorption bands in the region of 0 0 0 which had previously been impossible. Some of the complexity in these bands has been shown to be due to a large Duschinsky effect involving the two lowest b 1 vibrations, ν 25 and ν 26. It has been shown that these vibrations have wavenumbers of 176 and 110 cm −1, respectively, in the X ̃ state, and 172 and 39 cm −1 in the A ̃ state. This last value shows how unresistent the molecule is in the A ̃ state to out-of-plane bending in the region of the five-membered ring. Other aspects of the vibrational complexity are due to the effect of ν′ 26 in increasing the barrier to tunnelling of the hydrogen-bonding proton in the A ̃ state contrasting with very little effect of ν″ 26 in the X ̃ state.