VIBRATIONAL CIRCULAR DICHROISM OF 1,3-DIDEUTERIOALLENE, CALCULATIONAL RESULTS
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Publisher:Ohio State University
We have developed a refined force field for allene starting from an ab initio quantum mechanical calculated force field and using vibrational data from five isotopomers. VCD calculations were done at the coupled oscillator, FPC, LMO. APT and a priori levels. The latter used three different basis sets and two gauge formulations. In terms of dipole strengths, the higher level calculations did better with the LMO being off for the C=C=C and the FPC being generally poor. In the absence of experimental VCD, the calculations were all compared to triple zeta level results with the a priori calculation in the distributed origin gauge. In detail, the models showed extensive disagreement, even for the CH stretches, However, the gross patterns were qualitatively present in all the calculations with the restrictions that only large VCD be considered and that only the net VCD over close lying bands be evaluated. While there is no doubt that the FPC is quantitatively inadequate for both dipolar and rotational strength analysis, these results imply that there may be a qualitative use for these simpler models if the proper restrictions are taken into account.
Author Institution: Department of Chemistry, University of Illinois at Chicago; Department of Chemistry, University of Southern California