A model Hamiltonian is proposed for bond-breaking electrochemical electron transfer to an adsorbed molecule. The theory is applied to a homonuclear molecule, and self-consistent equations are derived for the occupation probabilities of the orbitals and the system energy. Model calculations result in an adiabatic potential energy surface with a minimum for the adsorbed state with the bond intact and a valley for the two dissociated anions. (c) 2005 Elsevier B.V. All rights reserved.