A VALENCE COUPLED OSCILLATOR MODEL FOR THE CALCULATION OF VIBRATIONAL CIRCULAR DICHROISM

Author Institution: Department of Chemistry, University of MinnesotaThe coupled-oscillator model is appropriate in a number of situations that arise in connection with vibrational circular dichroism (VCD). One such situation is where the normal modes of interest may be adequately described in terms of a set of isolated degenerate (or quasidegenerate) oscillators which couple principally among themselves. Frequently, the coupling mechanism is not specified and the interaction terms in the secular equation are taken as empirical parameters. In this work we show how they may be estimated from a valence force field. A particular case of interest is where the oscillators interact only indirectly by G and/or F matrix coupling to other coordinates. These indirect second-order interactions can be transformed so as to appear as direct couplings among the oscillators via a Van Vleck transformation. Dipole and rotational strengths may then be calculated from the resulting eigenvectors in conjunction with the local transition diploes and their relative geometry