Simulation of IRRAS Spectra for Molecules on Oxide Surfaces: CO on TiO2(110)

We explore a method that can simulate infrared reflection–absorption spectroscopy (IRRAS) spectra for molecules adsorbed on semiconductor surfaces. The method makes it possible to directly correlate experimental spectra with possible adsorbate structures. Our example in this paper is CO adsorbed on rutile TiO2(110). We present simulated IRRAS spectra for coverages in the range from 0.125 to 1.5 monolayer (ML). An explanation is provided for the apparent inconsistency in the literature concerning the tilting geometry of 1 ML CO on this surface. We find that a tilted structure (which is also the lowest-energy configuration) generates IRRAS spectra in excellent agreement with the experimental spectra. Furthermore, we predict the adsorption structure for 1.5 ML CO coverage over TiO2(110), which consists of very weakly bound CO molecules on top of the monolayer. In all cases, our simulation method, which is based on density functional theory (DFT) vibrational calculations, produces s- and p-polarized IRRAS spectra in excellent agreement with the experimental spectra.