Total van der Waals Interactions between Polar Molecules

Total van der Waals Interactions between Polar Molecules 

We have seen, now, that there are three types of interactions that can be involved in the total van der Waals interaction between atoms or molecules dipole-dipole (orientational or Keesome), dipole-induced dipole (induced or Debye), and dispersion (London) interactions. The theories for all three interactions are found (to a first approximation) to involve an inverse 6th power of the distance separating the two interacting centers. The total van der Waals interaction potential, Wvdw(r), can then be written as 

For two identical molecules the full equation takes the form 

Some representative values for total van der Waals interactions are given in Table 4.4. 

One can see from Table 4.4, the dispersion force contribution to the total van der Waals interaction can be quite significant. Except for very small and very polar molecules such as water, the dispersion force will exceed the Kee-som and Debye contributions and dominate the character of the interaction, even in the case of two dissimilar molecules. 

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