AB-INITIO CALCULATIONS OF ANHARMONIC VIBRATIONAL CIRCULAR-DICHROISM INTENSITIES OF TRANS-2,3-DIDEUTERIOOXIRANE

A priori theory is derived for anharmonic calculations of vibrational circular dichroism (VCD). The anharmonic VCD expression is gauge origi n independent and reduce to the magnetic field perturbation theory exp ression in the double-harmonic approximation. The theory has been impl emented using second-order contact transformations for the vibration p roblem, Zeroth, first, and diagonal second derivatives of the atomic a xial tensor are needed at the molecular equilibrium geometry. Ab initi o calculations have been carried out for trans-2,3-dideuteriooxirane u sing self consistent field theory for the atomic axial tensors and usi ng second-order Moller-Plesset theory for the atomic polar tensors and the force fields, The changes of the vibrational rotatory strengths f rom anharmonicities are small, and do not explain the previously obser ved large discrepancies between the double-harmonic results and the ex perimental values for three out of the 15 vibrational modes. (C) 1995 American Institute of Physics.