The process of dissociative adsorption of a molecule on an electrode in a system of the type in situ scanning tunneling microscopy (STM) is investigated theoretically. It is shown that, in the case of fully nonadiabatic or partly adiabatic electron transfer, the presence of the tip of STM may either accelerate (or even induce) or decelerate the process of dissociation of the molecule, depending on the sign of the bias voltage. The maximum effect takes place in the case of strong interaction of the molecule with both electrodes (fully adiabatic electron transfer). In this limit, diagrams of kinetic modes, which mark off the boundaries between processes of different types possible in a given system, are constructed.