Vibrational Excitons in CH-Stretching Fundamental and Overtone Vibrational Circular Dichroism Spectra

摘要

A set of vibrational circular dichroism (VCD) spectra in the CH-stretching fundamentalregion for about twenty compounds belonging to the class of essential oils was empirically analyzed bythe use of a sort of vibrational exciton mechanism, involving three centers. Through a general formulaapplicable to many coupled dipole oscillators, the rotational strengths of the previously identifiedvibrational excitons are evaluated. The results are then critically reviewed by the use of recent abinitio methodology, as applied to selected molecules of the original set. Further insight is gained bymodel calculations adding up the contribution of the coupling between electric dipole moments associatedwith normal mode behavior and that of the polarizability from polarizable groups. The formerpart is responsible for the excitonic behavior of the VCD spectra. For the same selected molecules wehave also investigated whether some excitonic behavior is taking place in the second overtone region,and have concluded that this is not the case.