INTERMOLECULAE FORCES AND INTERACTION ENERGY 



The potential energy of the ion and this dipole is thus: 



cp = - 



-«>. 



o- 



SkTd'D' 



.-f " 





/\Q +q 



d "^d 



0= '' 



6h 



0=0 



= -"" 



d^D 



Fig. 6-3. Interaction of an ion with a dipole. 



209 



(6-11) 



This apphes particularly to situations where the electrostatic potential 

 energy is small compared to kT\ when it is larger than kT the dipole will 

 be essentially oriented in the position of minimal energy and the potential 

 energy will be given approximately by — qjujd'^D. 



Dipole moments are usually expressed in electrostatic units. Thus if 

 each of the charges in a dipole is half an electron charge and the distance 



