Theory of Raman scattering by molecules adsorbed at electrode surfaces. Model calculations for resonance Raman scattering by an adsorbed diatomic

Model calculations of the resonant Raman cross section of a homonuclear diatomic adsorbate on a metallic electrode surface are performed. If the excited intermediate electronic state is weakly dipole coupled to the electronic ground state (relative to some other excited electronic states), electric field induced intensity borrowing is found to be very large for the adsorbate. The important excited state involved is that describing charge transfer from adsorbate to the metallic substrate. We have also carried out a simplified calculation of the vibrational Franck-Condon factors for the adsorbate. Combining electronic with vibrational enhancement factors, we find that there may be an overall intensity enhancement for the adsorbate of 10⁴-10⁸ depending on the electric field strength.