Abstract

Optical IR-Visible sum-frequency generation (SFG), a surface vibrational spectroscopy, has been used to study competitive adsorption at a hydroxylated ZrO₂ surface in contact with a number of binary solutions. This technique is similar to surface second harmonic generation (SHG) in that it is forbidden (in the dipole approximation) in spatial regions possessing inversion symmetry. Therefore, systems consisting of an interface bound by centrosymmetric media give rise to a nonlinear response which is dominated by that of the interfacial region. In addition to being surface specific, the SFG signal from the liquid/solid interface can be resonantly enhanced when the incident IR laser source used in the generation process is tuned through a vibrational mode in the adsorbed species, provided the mode is both Raman and IR active. This vibrational information allows identification of the adsorbed molecule as well as measurements of surface coverage, molecular orientation, and adsorbate interactions for a number of the two-component liquid systems.

© 1991 Optical Society of America