Magnetic Circular Dichroism of Molecules in Dense Media: Benzene

Abstract

The vibrational structuring in spectra of absorption and emission (1, 2), of circular dichroism (3), and of optical rotation (4-6) is of current interest. In this communication, we report some preliminary results of vibrational structuring in the magnetic circular dichroism (MCD) of benzene, and their tentative interpretation. In Fig. 1 is shown the MCD of benzene in the wavelength range of about 230-270 nm, corresponding to the 'A,0 --B2. transition. It is well known that the electronic transition 'A,0 --lB2,, is symmetryforbidden, but vibronic-allowed.We have discussed (7) the role of electronic and nuclear motion of molecules in their MCD, and have shown that in the adiabatic approximation the band shape of MCD is mainly determined by nuclear motion, while the electronic portion of the system is responsible for the strength of MCD. The expression for MCD for symmetry-forbidden but vibronic-allowed transitions can be written (7,8) BvT ,Av) (3) and Dj -Pv()(AV1Qj10A) = E PV V)(XAVrjQjIXAv,) (4)