Raman optical activity of molecules adsorbed on metal surfaces: Theory

The circular intensity differences (CID) in a Raman Optical Activity experiment for molecules adsorbed on metal surfaces are derived. Statistical averages are computed for the cases of complete orientational randomness and of adsorption with an axis fixed normal to the surface, and random orientation in the plane parallel to the surface. Unusually large CID values are expected provided that: (i) the electric field near the surface changes over distances much smaller than the wavelength of the incident light, and (ii) the gradients of the field have different phases than the field itself, or (ii') the molecular polarizability tensors have an imaginary part. These conditions should be met in realistic systems, especially in systems that exhibit surface enhanced Raman scattering.