The Position-Dependent Reaction Force Constant in Bond Dissociation/Formation

The concept of a position-dependent reaction force constant κ(R) can be used to distinguish the two phases of bond dissociation or formation: stretched bond, κ(R) > 0, and interacting but separate fragments, κ(R) < 0. The transition between these phases is at κ(R) = 0, which coincides with the minimum (for dissociation) or maximum (for formation) of the reaction force. As was shown earlier, all of these occur (for diatomic molecules) at the separation R at which the system's energy relative to equilibrium is about 27% of its dissociation energy.