Monitoring electronic structure changes of TiO2(110) via sign reversal of adsorbate vibrational bands.

The adsorption of NO on single crystalline rutile TiO(2)(110) surfaces at 100 K and the subsequent formation of N(2)O via NO dimer intermediates was studied by reflection-absorption infrared spectroscopy using a UHV-FTIR system. Analysis of the IR data reveals that the occurrence of s-polarized adsorbate vibrational bands always increases the reflectivity, giving negative bands, whereas p-polarized bands are either positive or negative, depending on the reduction state of the substrate. This sign reversal of optical bands is caused by vacancy doping, which also affects the optical constants governing the complex interplay between reflection and transmission of p-polarized light on a dielectric substrate.