A density-functional study of the atomic structures and vibrational spectra of NO/Pt(111)

We performed ab initio plane-wave calculations for NO/Pt(111) using a slab model. The results show that at a low coverage of 0.25 ML, the fcc-hollow site is the most stable adsorption site. Our calculations at a higher coverage of 0.50 ML indicate that NO molecules prefer to be adsorbed at both fcc-hollow and atop sites rather than only at hollow sites. This adsorption arrangement is consistent with a recent scanning tunneling microscopy experiment. The calculations of the peak intensities of fcc-hollow and atop species reveal that the peak corresponding to the fcc-hollow species becomes very small in the presence of the atop species. This effect turns out not to be due to the well-known intensity-transfer effect derived from the dynamic dipole-dipole coupling, but to be related to a change of the electronic state of the adsorption system by the addition of the atop species. This conclusion warns experimentalists using vibrational spectroscopy that spectra they measure should be interpreted very carefully. (C) 2002 Elsevier Science B.V. All rights reserved.