Free electron levels in catalysis

Using the MO LCAO method in the Hückel approximation, we show that under certain conditions the heat of adsorption of an activated complex on the acceptor centre of a catalyst may become greater than the heat of adsorption of the original molecules. This means that the activation energy of the molecular reaction decreases under the influence of the donor-acceptor bond. The symmetry of the wave functions of the active centers and of the upper filled level of the activated complex and the relationship between the energy levels are of considerable importance. A decrease in the activation energy is facilitated by having the free level of the acceptor in the lowest possible position, and also by increasing the distance between the upper filled levels of the activated complex and the original molecules.