Methanol Adsorption on TiO₂ Film Studied by Sum Frequency Generation Vibrational Spectroscopy (cited:2)

A broadband infrared surface sum frequency generation vibrational spectroscopy (SFG-VS) and an in situ UV excitation setup devoted to studying surface photocatalysis have been constructed. With a home-made compact high vacuum cell, organic contaminants on TiO₂ thin lm surface prepared by RF magnetron sputtering were in situ removed under 266 nm irradiation in 10 kPa O₂ atmosphere. We obtained the methanol spectrum in the CH₃ stretching vibration region on TiO₂ surface with changing the methanol pressure at room temperature. Features of both molecular and dissociative methanol, methoxy, adsorbed on this surface were resolved. The CH₃ symmetric stretching vibration frequency and Fermi resonance of molecular methanol is red-shifted by about 6?8 cm^-1 from low to high coverage. Moreover, the recombination of dissociative methanol and H on surfaces in vacuum was also observed. Our results suggest two equilibria exist: between molecular methanol in the gas phase and that on surfaces, and between molecular methanol and dissociative methanol on surfaces.