Infrared Spectra of Alkylphosphonic Acid Bound to Aluminium Surfaces



Summary: The infrared absorption (IR) spectrum of alkyl phosphonic acid adsorbed on the α-Al2O3 (0001) surface has been calculated by means of a density-functional based tight-binding method. Thereby mono-dentate, bi-dentate and tri-dentate bonding of the acid to the surface have been considered. In addition, experimentally obtained Fourier Transform Infrared Spectra (FTIR) of octadecylphosphonic acid (ODPA) on the natural surface of aluminium have been included. The absence of the P[DOUBLE BOND]O band in the experimental surface spectrum and in the calculated spectrum of the tridentate adsorption complexes showed that adsorption of (alkyl)phosphonic acids on aluminium favours tridentate bonding, where the acid is bound to the surface via three symmetric P[BOND]O[BOND]Al bonds.