VIBRATIONAL CIRCULAR-DICHROISM OF PROPYLENE-OXIDE

Vibrational absorption and circular dichroism spectra of neat liquid and CS2 and CCl4 solutions of propylene oxide are reported. Scaled quantum-mechanical (SQM) force fields are derived from absorption frequencies together with ab initio SCF calculations using the STO-3G, 4-31G, 6-31G*, and 6-31G** basis sets. Absorption and VCD spectra are calculated using these force fields and ab initio SCF atomic polar and axial tensors obtained using analytical derivative methods and STO-3G, 4-31G, 6-31G*, 6-31G**, DZ/1P, and 6-311G** basis sets. Atomic axial tensors are calculated using two choices of gauge. Calculated spectra are in generally excellent agreement with experiment when basis sets of sufficient size are used for the calculation of force fields and atomic polar and axial tensors and when the distributed origin gauge is used. Agreement is less satisfactory in spectral regions where vibrational transitions are closely spaced and where Fermi resonance is substantial. The results support the conclusion that generally reliable predictions of VCD spectra can be obtained using Stephens' equation for vibrational rotational strengths together with molecular geometries, vibrational force fields, and atomic polar and axial tensors derived via ab initio SCF calculations.