Knowledge Bank

Vibrational circular dichroism (VCD) and infrared intensities have been calculated for the CH stretching modes of alanine-$Nd3$, alanine-$C\ast d1Nd3$ and alanine-$Cd3Nd3$ and using the localized molecular orbital [LMO] model. Calculated rotational strengths were found to be in close agreement with experiment in both sign and magnitude, differing by at most a factor of two. The calculations were based on the same refined Urey-Bradley force field used in the calculations using the fixed partial charge (FPC) model described in the previous paper. The significance of these results in relation to the prediction of VCD results particularly in cases where FPC calculations give rotational strengths which are too small will be discussed. In particular, the importance of the motion of electronic charge as described by the centroids of localized molecular orbitals will be explained and stereo-projections of the nuclear and orbital displacements from equilibrium for the various normal modes will be shown. Finally, detailed comparisons of simulated LMO-VCD spectra will be compared to the experimental spectra.