Dissociation of Polyatomic Molecules and the Relation of Ensuing Geometrical Change to the Force Constants

As a triatomic molecule dissociates to give a diatomic molecule and an atom, the length of one bond must change as a function of the extension of the other, becoming eventually the length of the bond in the diatomic molecule. If this change is assumed to be monotonic, there follow two rules: Both bonds in the triatomic molecule must be longer, or both must be shorter, than the bonds in the diatomic molecules, and, if they are both longer, the quadratic interaction force constant is positive, otherwise it is negative. These rules are tested with a number of experimental data. The rules are also extended to more-than-three atomic molecules.