CO adsorbed to NaCl(100) exhibits perhaps the weakest possible coupling between the adsorbate and solid. It is, therefore, an ideal system to observe the influence of adsorbate-adsorbate interactions on infrared absorption. In this work, we report polarized FTIR absorption spectra of CO/NaCl(100) as a function of coverage (0.02 <= theta <= 1 ML), where the coverage has been quantitatively determined by temperature-programmed desorption and molecular beam dosing. We extend a previous semi-empirical model designed to describe the screening of the local electric field due to dipole-dipole interactions in a CO monolayer. The extended model applies to sub-monolayer coverages and describes properly the electric field of the absorbed radiation at the vacuum-substrate interface. Fitting this model to coverage-dependent IR absorption data allows us to derive the vibrational and electronic polarizabilities chi (v) = 0.0435(14) angstrom (3), chi (e) = 3.30(36) angstrom (3) and the integrated absorption cross section of 2.51(8) x 10(-17) cm/molecule for an isolated CO molecule adsorbed at the NaCl (100) surface. The determined integrated absorption cross section is substantially smaller than that of gas phase CO.
展开▼
