Adsorption and dissociation of water on LaB6(100) investigated by surface vibrational spectroscopy

Abstract

The chemisorption of water (H2O and D2O) on a LaB6(100) surface was studied with reflection absorption infrared spectroscopy (RAIRS) and high resolution electron energy loss spectroscopy (HREELS). The clean surface was exposed to H2O and D2O at temperatures from 90K to room temperature, and spectra were acquired after heating to temperatures as high as 1200K. It was found that water molecularly adsorbs on the surface at 90K as a monomer at low coverages and as amorphous solid water at higher coverages. Water adsorbs dissociatively at room temperature to produce surface hydroxyl species as indicated by OH/OD stretch peaks at 3676/2701cm−1. Room temperature adsorption also reveals low frequency loss features in HREEL spectra near 300cm−1 that are quite similar to results obtained following the dissociative adsorption of O2. In the latter case, the loss features were attributed to the LaO stretch of O atoms bridge-bonded between two La atoms. In the case of dissociative adsorption of H2O, the low frequency loss features could be due to either the LaO vibrations of adsorbed O or of adsorbed OH.