Field Dependent Chemisorption and the Interfacial Stark Effect General Relationships

Field Dependent Chemisorption and the Interfacial Stark Effect General Relationships 

It is a natural tendency of electrochemists to be interested in the potential or electric field dependence of a chemisorption bond, hi particular, electrochemists would like to know how the nature of the chemical bond, its coordination to the surface, the bond strength, and vibrational frequencies, both substrate-adsorbate and intramolecular, depend on the electrode potential. In recent years, some general rules concerning field-dependent chemisorbate bonding have emerged from extensive DPT calculations, and it is the aim of this section to review these advances. 

Equation (14) shows that the static dipole moment /4 describes, to a first approximation, the field dependence of the bond strength, i. e.  

As binding energies, and hence their field dependence, are difficult to measure experimentally in an electrochemical cell, it is of interest to examine the field dependence of other fundamental binding characteristics, in particular vibrational properties of the chemisorbate. A fundamental equation for the field dependence of a vibrational frequency can be straightforwardly derived from Eq. (14). The force constant Kf at field F can be obtained by determining the minimum of Eq. (14) at field F and then inserting the resulting value for Ar in the expression for the second derivative of E with respect to Ar. This yields  

From a generalization of these equations, an expression for the slope of the force constant and the vibrational frequency at field F can be derived, i. e. 

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