A quantum-chemical study of pyridine adsorption on the surface of a charged mercury electrode

The interaction of a pyridine (Py) molecule with the surface of a charged m ercury electrode was studied by the ab initio Hartree-Fock-Roothaan method. The electrode was modeled by a planar seven-atomic Hg-7 cluster with a sig ma = +/- 12.5 muC/cm(2) surface charge density. The electronic properties o f the [Hg-7(+/-). . . NC5H5] system were studied, the energy profiles of py ridine adsorption on the charged mercury surface were constructed, and the energies of adsorption were calculated. The dependence of the total energy of the adsorption system on the r(Hg-Py) distance is characterized by the d eepest minimum if the charge density is positive and Py interacts with the metal through the lone pair on nitrogen. At a positive surface charge (sigm a > 0), the vertical orientation of the adsorbate molecule is energetically favorable, whereas if the surface charge is negative (sigma < 0), adsorpti on does not occur.