Hydrogen-bond induced surface core-level shift in pyridine carboxylic acids

Intermolecular hydrogen bonding in thick films of pyridine carboxylic acids (isonicotinic, picolinic and bi-isonicotinic acid) evaporated onto rutile TiO₂(1 1 0) has been investigated with X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. These molecules are shown to be strongly H-bonded in the condensed phase, and a surface core-level shift is observed due to the presence of non-H-bonded nitrogen atoms in the surface layer. Density functional theory calculations are used to relate the experimental data to the proposed bonding configurations based on the surface termination of the known equilibrium solid-state structure. A kinetic barrier, attributed to the high degree of molecular orientation required for the formation of extended H-bonding networks, has also been investigated.