Knowledge Bank

Vibrational Circular Dichroism (VCD) spectra in the CH-stretching overtone region (up to $\Delta v=6$) have been observed for cyclic molecules with relatively low barrier torsional twisting or puckering modes (a). This has motivated us to perform classical trajectory calculations on a three-degrees of freedom model of the HCCH fragment, where the optical activity of the molecules is thought to come from. The three degrees of freedom are the two CH-stretchings and the torsional mode around the CC bond. Two cases are considered differing mainly on the barrier height V to the hindered rotation: $V=200cm-1$ representing (3R)-Methylcyclopentanone-type HCCH fragments, $V=2000cm-1$ representing Limonene-type HCCH fragments. Poincar'{e} surfaces of sections and Fourier cross spectra (b) have been generated in order to interprete the observed VCD spectra.