Fermi resonance in the ν8:ν1 + ν6 ground state diad and relative vibronic activity of the ν8 and ν6 vibrations in the [formula omitted] system of benzene

Abstract

Using the known resonance parameters determined from the ionisation detected Raman spectrum of the ν8:ν1+ν6 Fermi resonance diad in the ground state, the intensity relations in the Fermi resonance diads 810:110610 and 810611:110621 in the benzene A∼1B2u-X∼1A1g system are analysed to give a value of+0.18 for the ratio of the first order Herzberg–Teller coefficients for the ν8 and ν6 vibrations in this spectrum. This leads to a figure of 0.012 for the relative vibronic activity (oscillator strength) of ν8 and ν6, which result is compared with current theoretical estimates. Some anomalies in the SVL fluorescence spectra of these Fermi resonance diads are discussed.