Probability theory of desorption kinetics of self-assembled alkanethiols stabilized with pair interaction

An electrode kinetic theory is presented for the reductive desorption of self-assembled monolayers of alkanethiols adsorbed on a Au(111) surface by taking account of the probability of pair interaction between closest neighboring all;yl chains. The model of the desorption is a honeycomb-arrangement unit of adsorption sites, the center of which is occupied by the alkanethiol to be desorbed. The six surrounding sites are occupied or not by alkyl chains, depending on the pair interaction energy. The probability of de-stabilizing the alkyl chains on the six sites is calculated for all the possible arrangements. On the assumption that the desorption kinetics have an exponential dependence on the potential, a non-linear kinetic equation is derived, from which voltammograms are obtained in terms of the interaction energy and two kinetic parameters. The peak potential varies linearly with the logarithm of the potential sweep rate. With a negative increase in the interaction energy, the desorption wave shifts linearly in the negative direction and it becomes narrower. Voltammograms for alkanethiols with several chain lengths were analyzed on the basis of these variations. The transfer coefficient is determined from the variation of the peak potential with the sweep rate. The pair interaction energy is evaluated from the variation of the peak potential with the chain length. (C) 1998 Elsevier Science S.A. All rights reserved.