Debye Force (Dipole-Induced Dipole Interaction)

The Debye force, also known as the induction force, explains how a polar molecule can attract a nonpolar one. A polar molecule possesses a permanent electric dipole, which creates an electric field in its vicinity. When a nonpolar molecule enters this field, its electron cloud is distorted—electrons are pushed away from the negative end of the dipole and pulled toward the positive end. This separation of charge creates a temporary, ‘induced’ dipole in the nonpolar molecule. The interaction is always attractive because the induced dipole is always oriented favorably with respect to the permanent dipole that created it.

Unlike the Keesom force, the Debye force is not dependent on temperature. This is because the induced dipole is created by the permanent dipole and follows its orientation instantaneously, so thermal tumbling of the permanent dipole does not average out the attraction. The strength of the Debye force depends on two factors: the magnitude of the permanent dipole moment ([latex]\mu[/latex]) of the polar molecule and the polarizability ([latex]\alpha[/latex]) of the nonpolar molecule. While generally weaker than dipole-dipole forces, Debye forces are essential for understanding the behavior of mixtures containing both polar and nonpolar components.