A constant characterizing the strength of the bond in a diatomic molecule. Near the equilibrium position, R_e, of the potential energy curve of a diatomic molecule, the potential energy V is accurately represented by a parabola of the form V = k/2(R – R_e)², where R is the internuclear distance and k is the force constant. The greater the force constant, the stronger is the bond between the atoms, since the walls of the potential curve become steeper. Regarding the molecular vibrations as simple harmonic motion, the force constant occurs in the analysis of the vibrational energy levels.