Correspondence between the reaction force minimum and the onset of abrupt variations of the kinetic and potential energies in bond dissociation and formation

We demonstrate that the minimum of the reaction force curve of a diatomic or polyatomic molecule undergoing bond dissociation is significant in several respects. As has been pointed out in the past, it is the point at which the force opposing dissociation is strongest. It marks the boundary between the primarily structural stage of a bond dissociation (stretching) and the transition region between the stretched bond and independent atoms. We now show that the reaction force minimum is also where the kinetic and potential energy curves tend to change direction abruptly. At this point, the total energy E(R) has increased by about 27% of the dissociation energy, for both diatomic and polyatomic molecules.

Dissociation curves are analyzed at the UHF/daug-cc-pV5Z level of theory using Gaussian 16.