INTERMOLECULAR FORCES AND INTERACTION ENERGY 



231 



minimum energy of interaction and this occurs at the equilibrium distance 

 dg. The equilibrium values may be obtained from Eq. 6-50 by setting 



d, = [aAlbBy'^-"^ (6-51) 



B 



u 



1-A 



a 



(6-52) 



Repulsion Correction Factors for the Interaction Energy 



In Fig. 6-6 it may be seen that the equilibrium interaction energy is 

 not that which would be calculated from the attraction equations previously 

 given in this chapter; the value so calculated is indicated by (pi,. The re- 

 lation between cp^ and 9"j may be given by: 



r(Pi, 



(6-53) 



where r may be termed the correction factor by which the calculated energy 

 must be multiplied to give the equilibrium energy. Since: 



n- - Bid 

 the correction factor is given by: 



(6-54) 



(6-55) 



The values for r assuming that a = 12 are given in Table 6-7 for the types 

 of interaction previously discussed; the corrected energy equations are 

 also presented for convenience in reference. 



These correction factors are applicable only to equilibrium distances. 

 At greater distances the necessary correction decreases rapidly. We shall, 

 however, be mainly concerned with (f^ and for estimating this interaction 

 energy the equations in Table 6-7 will be used. Despite the admittedly 

 approximate nature of these equations, they may be useful as a basis for 

 more accurate formulations. 



When two types of attraction must be considered: 



B 



If 



and the equilibrium energy is given by: 



B 



1} 



(6 70) 



(6-71) 



Thus (p^ may be obtained from the attraction energy cp^^ by multiplying 

 each of the terms by the respective correction factor given in Table 6-7. 



