Vibrational spectroscopy of adsorbates on the (111) and (100) surfaces of lanthanum hexaboride

Reflection absorption infrared spectroscopy has been used to study the adsorption of carbon monoxide, oxygen, and decaborane on the (100) and (111)adsorption of carbon monoxide, oxygen, and decaborane on the (100) and (111) surfaces of lanthanum hexaboride. Exposure of the surface at temperatures of 95 K and above to O₂ produces atomic oxygen on the surface and yields vibrational peaks in good agreement with those observed previously with the technique of high resolution electron energy loss spectroscopy (HREELS). As in the previous HREELS studies, the peaks observed in response to oxygen adsorption are assigned to vibrations of the B₆ octahedra that gain intensity due to a decrease in electronic screening of surface dipoles. In the case of CO, molecular adsorption occurs at 95 K and gives rise to a variety of C-O stretch peaks, depending on adsorption site.Decaborane adsorbs molecularly at 95 K and gives rise to intense peaks in the B-H stretch region that evolve with annealing temperature into a single peak at 2571cm^-1 due to an unidentified surface intermediate possessing BH bonds.