Theoretical DFT study on the interaction of NO and Br₂ with the Pt(111) surface

Density functional calculations were performed at the B3LYP level using combined basis sets for the NO and bromine interactions with the Pt(111) surface mimicked by the two-layer Pt₁₀ cluster model. It explains well an attractive bonding interaction not only for bromine and Pt(111) but also for all three adsorption modes of NO on the Pt(111) surface. In accordance with the experimental observations, the calculations predict that the first peak in the IR spectra appears at around 1515 cm^-1 at the initial stage of low NO coverage, while it would shift to 1707 cm^-1 at high NO coverage. The bonding of NO on the 3-fold hollow fcc and hcp sites of Pt(111) proceeds via predominant back-donation interactions, while for the on-top adsorption, both the donation and back-donation interactions become equally important. Energetic criteria show also that the STM tip (made from Pt and Ir alloys) immersed into a bromine solution may contain only dissociated bromine atoms that bind strongly with the surface Pt atoms. As a result, the ν_BrBr stretching vibration mode for the bromine molecule may not be seen in the IR spectra because of its dissociation into adsorbed atoms. This leads to an appearance of a blue shifted band centered at ca. 202 cm^-1.