A 2ND-HARMONIC GENERATION ANALOG OF OPTICAL-ROTATORY DISPERSION FOR THE STUDY OF CHIRAL MONOLAYERS

Surface second harmonic generation (SHG) is shown to display optical r otatory effects dependent on the handedness of chiral molecules (2,2'- dihydroxy-1,1'binaphthyl) at various interfaces. The polarization of t he surface SHG radiation is rotated with respect to that of the input fundamental radiation in a direction indicative of the chirality of th e surface molecules. The origin of SHG-ORD lies in the electric dipole -allowed chi(2) tenser elements, one of which is associated with the h andedness of surface species. The SHG-ORD rotation is independent of t he density of surface species for an optically pure system, but is dep endent on the chiral excess for mixtures of enantiomers. It is wavelen gth dependent but resonance is not required to observe the rotation. T he experiments show that while SHG-ORD has origins quite distinct from ordinary ORD, it can be utilized to measure chiral structures of surf aces.