Fermi resonance structure in the CH vibrational overtones of CD3CHO

Abstract

Gas-phase fundamental and CH and CO overtone spectra (700–17 500 cm−1) of 2,2,2-trideuteroacetaldehyde were recorded using FTIR and laser photoacoustic techniques. The Fermi resonance structure in the overtone spectra of the coupled CH stretching and in-plane CH bending vibrations is analyzed with a tridiagonal Hamiltonian, yielding a large effective coupling constant, ‖k′sbb‖ =93 cm−1, corresponding to subpicosecond redistribution times. No coupling between the out-of-plane CH bending mode and the Fermi resonance system is apparent. This study presents the first detailed analysis of the anharmonic couplings in the CH chromophore at an sp2 carbon atom. The in-plane CH bending vibration couples in a manner similar to the CH(sp3) bending vibrations, whereas the out-of-plane bending vibration is decoupled, similar to the CH(sp) bending vibrations.