Superexchange nonresonant tunneling current across a molecular wire

A modified superexchange model for the formation of nonresonant tunnel current through a molecular wire consisting of a regular chain and terminal units is developed. Under conditions of weak mixing of the localized terminal molecular orbitals with the delocalized orbitals of regular chain, the explicit expressions for the tunneling current are obtained and the conditions for the applicability of the superexchange model are found. It is shown that in limiting cases, the attenuation factor for the tunneling current coincides with that used for analysis of experimental data within the framework of the rectangular barrier model or the “deep” tunneling model. Using the modified superexchange model, the experimental data on the dependence of the currentvoltage characteristics of the N-alkanedithiol molecular wire on the number of C-C bonds are interpreted, and the conditions are formulated for which the simplest model of a rectangular barrier with a tunneling effective electron mass can be used for the analysis of experimental data.