SFG study of formic acid on a Pt(110)-(1 × 2) surface

Abstract Infrared-visible sum frequency generation (IR-vis SFG) spectroscopy, infrared reflection absorption spectroscopy (IRAS), and temperature programmed desorption (TPD) spectroscopy were used to investigate the systems prepared by the adsorption of formic acid (HCOOH) onto a Pt(110)-(1 × 2) reconstructed surface. In the SFG spectra, we observed that several vibrational bands which can be assigned to the CH stretching, the OH stretching and combination modes of formic acid adsorbed in multilayers show a strong dose temperature dependence. From the IRAS measurements, it was found that the formic acid adsorbed in multilayers forms the chain structure which is called the α-crystalline form. By combining the results of the dose temperature dependence of SFG spectra with that of IRAS spectra, we conclude that the length of the chain, the orientation of the chain axis, and the size of the single crystalline region of formic acid strongly depend on the dose temperature. Furthermore, we found that the SFG signal of the CH stretching band shows the intensity oscillation during the exposure to formic acid.