Relative Intensities of Nonequivalent CH Bonds in the Local Mode Overtone Spectra of 1,3- and 1,4-Cyclohexadiene

Abstract

The CH stretching overtone spectra of 1,3- and 1,4-cyclohexadiene have been recorded in the regions corresponding to Δv = 2−6. Bands are assigned as overtones of the various nonequivalent CH bonds. Oscillator strengths have been calculated according to the harmonically coupled anharmonic oscillator (HCAO) local mode (LM) model, with ab initio dipole moment functions. The theoretical values have been compared to experimental values, and good agreement is found between predicted intensities and measured relative intensities within an overtone band. For 1,4-cyclohexadiene, shoulders were observed approximately 100 cm-1 above and below the pure LM transition for Δv ≥ 4. These are assigned as (±) combinations with a low-frequency ring-puckering mode.