Intermolecular Interactions in Hydrocarbons

The nature of intermolecular interactions is exemplified by the crystal structures of polycycUc aromatic hydrocarbons (PAHs) which contain only carbon and hydrogen atoms. Analyses of crystal structures have led to the derivation of numerical constants describing the forces between pairs of atoms [11,12]. Thus the potential energy expression involves an equation of the form 

In this equation rjkis a nonbonded interatomic distance between atoms j and k, q is the point electrostatic charge on an atom, and Aj Bj and are adjustable parameters that have been obtained from experimental measurements of unit cell dimensions, interatomic distances, and packing arrangements in crystal structures. Ajk represents the coefficient of ffie London dispersion attraction term between atoms j and k, while Bjk and Cjk are short-range repulsive energy terms. The summation is over all interatomic interactions (between all j atoms and all k atoms). For PAHs the terms in Eq. (1) represent forces between pairs of 

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