Combined multidimensional anharmonic and parity violating effects in CDBrClF

Abstract

Parity violation causes rovibrational frequency shifts in infrared and microwave spectra between the corresponding lines of enantiomers of chiral molecules. In previous theoretical treatments of this effect simple harmonic and anharmonic adiabatic approximations were used which assumed that the vibrational potential as well as the parity violating potential are separable in normal (or local) coordinates. In the present work we investigate in detail the influence of nonseparable anharmonic couplings on vibrational frequency shifts caused by the parity violating potential in CDBrClF. We use the strongly coupled four-dimensional CD- and CF-chromophore subspaces and discuss how relative frequency shifts are influenced by coupling in the pure vibrational potential as well as in the parity violating potential. A four-dimensional parity violating potential energy hypersurface has been determined ab initio and fitted to a polynomial expansion. We analyze the nonseparable multidimensional representation of the parity violating potential in a chiral molecule. The effects of the multidimensional anharmonic couplings provide the dominant corrections. They are found to be about 20% for the expectation value of the parity violating energy difference ΔpvE between enantiomers (coupled ΔpvE/hc≈1.76×10−12 cm−1 compared to 1.96×10−12 cm−1 uncoupled). The corrections due to anharmonic multidimensional coupling can be more than a factor of 2 for vibrational frequency shifts, depending on the mode considered.