Adsorption and dissociation of water on LaB[sub]6(100) investigated by surface vibrational spectroscopy

The chemisorption of water (H[sub]2O and D[sub]2O) on a LaB[sub]6(100) surface was studied with reflection absorption infrared spectroscopy (RAIRS) and high resolution electron energy loss spectroscopy (HREELS). The clean surface was exposed to H[sub]2O and D[sub]2O at temperatures from 90 K to room temperature, and spectra were acquired after heating to temperatures as high as 1200 K. It was found that water molecularly adsorbs on the surface at 90 K 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 3676/2701 cm[super]-1. Room temperature adsorption also reveals low frequency loss features in HREEL spectra near 300 cm[super]-1 that are quite similar to results obtained following the dissociative adsorption of O[sub]2. In the latter case, the loss features were attributed to the La[inline image]O stretch of O atoms bridge-bonded between two la atoms. In the case of dissociative adsorption of H[sub]2O, the low frequency loss features could be due to either the La[inline image]O vibrations of adsorbed O or of adsorbed OH.