Adsorption of polar molecules on a molecular surface

Calculations are presented on the electrostatic potential modification arising from molecular adsorbates on a molecular monolayer. Analysis at the ab initio level indicates that the overall dipole moment of the bimolecular monplayer-adsorbate complex formed on physisorption is dominated by the dipole moments of the individual molecules, with a small correction due to charge transfer. The induced dipole moment is greatest with more polarizable molecular monolayer constituents such as p-nitroaniline. Additionally, numerical simulation shows that the average electric field across the adsorbing surface increases linearly with the number of adsorbed analyte molecules and exhibits an inverse dependence on the thickness of the monolayer. This thickness dependence indicates a long-range effect of the dipole layer resulting from the two-dimensional nature of the system.