<title>Infrared-visible sum frequency generation spectroscopy applied to adsorption and reaction at solid surfaces</title>

Abstract

Infrared-vision sum frequency generation (IR-vis SFG) spectroscopy and temperature programmed desorption (TPD) spectroscopy were used to investigate the systems prepared by the adsorption of formic acid onto MgO(001) and Pt(110) surfaces. Prominent vibrational bands observed on the SFG spectra were located at 2870 cm<SUP>-1</SUP> on the MgO surface and a 2960 cm<SUP>-1</SUP> on the platinum surface, which were assigned to the CH stretching band of formate ion (HCOO<SUP>-</SUP>) produced by the dissociative adsorption. On the MgO surface, three different sites, produced by the repetition of adsorption-thermal desorption cycles, were identified as responsible for the adsorption. The tilt angle of the CH group was estimated from the polarization characteristics of SFG signals and was derived as 0 degree(s) +/- 30 degree(s) for the group giving dominant SFG peak. On the Pt(110) surface, at least six vibrational bands were identified on the SFG spectra, and the temperature dependence indicated that the orientation of formate molecules changed right before their desorption. Expressions of SFG tensor components of a diatomic molecule were derived.