Adlayer structures of pyridine base molecules over zeolite (010) surfaces: a semi-empirical study based on AFM observations

The molecular array structures and molecular orientations within the adlayers of pyridine base molecules (pyridine and β-picoline) liquid-phase-adsorbed on (010) surfaces of natural zeolites (heulandite and stilbite) determined by in situ atomic force microscopy (AFM) were examined by semi-empirical molecular orbital calculations. All the adlayers studied possess (quasi-)hexagonal array structures, with different two-dimensional lattice constants for different adsorption systems. The AFM-observed array structures were close to the calculated energy minima with respect to their unit cell dimensions. The AFM-observed molecular orientation within the β-picoline adlayer was also energetically the most favourable among possible molecular orientations. Molecular tilt angles, which were not determined by AFM, were estimated by the semi-empirical calculations.