Abstract
A new principle of steady state of atoms in heteronuclear diatomic molecules based on constraint rule is proposed. Each atom in a heteronuclear diatomic molecule is described by three parameters a, b and ζand the atoms are the most stable when the value ζa/b is constant(2.601824). This model has one free parameter which was fitted by the graphical method.The calculated dissociation energy are in good agreement with the known experimental values.