CHARGE-TRANSFER EFFECT ON SURFACE-ENHANCED 2ND-HARMONIC GENERATION

Surface-enhanced second-harmonic generation (SESHG) arising from elect rochemically roughened silver surface adsorbed molecules has been inve stigated. The repetitions of electrode potential sweep in the nonfarad aic region were observed to cause irreversible losses in the optical s econd-harmonic signal. The SESHG intensity profiles obtained in the pr esence of adsorbates were seen to depend on the electrode potential. W e interpret the dependence of the SESHG intensities on the electrode p otential as a charge-transfer effect. It is suggested that the resonan t excitation of the charge-transfer transition enhances the second-har monic generation intensities. A charge-transfer calculation is used to fit the data for the effect of electrode potential on the intensities . It is found that the second-harmonic intensity profile predicted in the calculation agrees very well with the experimental values.