Surface CARS spectroscopy of pyridine and phenol on ZnO optical waveguides

Abstract Using planar optical waveguide geometry, surface CARS spectra of phenol and pyridine adsorbed on ZnO surfaces have been observed under high-vacuum conditions. When most of the CARS contribution from the ZnO film was eliminated by an interference condition, submonolayer quantities were detectable. The v 12 mode of phenol is insensitive to the nature of the surface bond and leads to a single line at 1002 cm −1 . The v 1 mode of pyridine gives rise to three lines at 993, 1000 and 1008 cm −1 corresponding to sites for physisorption, hydrogen-bonding and protonation. At high surface power densities, photoinduced desorption of pyridine was observed. Two-photon absorption in the ZnO leads to a power-dependent index of refraction.