Vibrational spectra of nitric oxide chemisorbed on Pt(100)

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Abstract
The chemisorption of NO on a Pt(100) single crystal surface at 140 and 300 K was investigated by high resolution electron energy loss spectroscopy, combined with Auger electron spectroscopy and LEED. Chemisorption of NO was predominantly molecular. The unreconstructed Pt(100)−1×1 surface was characterized by a single NO stretch frequency at 1615 cm−1 and two low frequency vibrations at 230 and 380 cm−1. These latter modes are likely to represent the Pt–NO stretch and Pt–N–O bending vibrations, respectively. The adsorbed molecule has therefore Cs symmetry in this case and is bent with respect to the surface normal. Low coverage NO adsorption at 140 K on the reconstructed Pt(100)−5×20 surface gave rise to three frequencies at 1690, 465, and 310 cm−1. Thus NO is also adsorbed in a bent configuration on this surface. At higher coverage an additional NO stretch frequency at 1790 cm−1 indicated a second adsorption site. Low frequency modes could not be clearly resoled for this species. NO adsorption on the same surface at 300 K was characterized by frequencies at 1805, 1630, and 380 cm−1, independent of NO coverage. At this temperature the reconstruction of the surface is lifted locally where NO adsorption took place. In analogy to the 1×1 surface it was concluded that the major NO state corresponds to a bent NO molecule while the 1805 cm−1 frequency represents NO adsorbed on a defect site which is created by the structure transformation.