Observation of gradual changes of the force constants in a system on the subsequent reaction steps on the way from reagents (RS) to products (PS) contains valuable information on the mechanism of this reaction, especially as the present analysis is focused on the electronic energy contributions to bonds. In our earlier work we have studied the evolution of H-F forces along IRC path and their the projection onto the reaction coordinate. The second energy derivative over the reaction progress (the reaction force constant) has been advocated