The Mechanism of Chromatographic Retention - Chromatographic Interactions > Dispersive Interactions > Page 4

The theory behind dispersive interactions is complex but it can be stated that the interaction energy, (UD), involved with such forces can be expressed as

 

where (ap) is the polarizability of the molecule,
(vo) is the characteristic frequency of the molecule,
(hp) is Planck's constant,
and (l) is the distance between the molecules.

The polarizability (a) is the crucial factor that controls the dispersive force acting on the molecule, which, for substances that have no dipoles, is given by

where (D) is the dielectric constant of the material
and (nv) is the number of molecules per unit volume.