A theory of the adiabatic interfacial electron transfer reactions is presented based on the exactly solvable surface molecule limit of the Anderson-Newns model. Unlike the other papers on this subject, the electron correlation effects are taken into account from the very beginning and exactly. It is shown that the electron correlation effects play an important role in the region of parameters describing adiabatic electron transfer and lead not only to quantitative corrections to the results obtained earlier in the spinless model or in the Hartree-Fock approximation but also to new qualitative effects. The critical regions, which correspond to different types of electron transfer processes, are obtained within the space of parameters of the model and classified. The corresponding kinetic regime diagram is constructed and presented. Examples of the adiabatic Gibbs energy surfaces for a number of characteristic, electrochemical electron transfer reactions are given and discussed.