Intermolecular interactions of aromatic hydrocarbons in carbonaceous materials: A molecular and quantum mechanics

Abstract

Aromatic hydrocarbons (PAHs and oligomers) that are models of carbonaceous materials components were studied using MM+All Atom Force Field and the semi-empirical methods (MINDO3 and ZINDO1) of quantum chemistry. The following intermolecular interactions were studied through potential energy function: (i) Among PAH molecules; (ii) among oligomeric molecules; and (iii) among oligomer and PAH molecules. (i) The potential energy minimized stacks of PAHs showed interlayer distances which correspond to the experimentally measured distances in carbonaceous materials. (ii) Interactions among oligomers, in general, resulted in aggregates that showed random space orientation of aromatic units. Only few aromatic units of separate oligomers were parallel to each other. (iii) Interactions among the oligomer and PAH molecules resulted in parallel orientation of PAH molecules relative to aromatic units of the oligomer. Common orbitals were found in stacks of parallel oriented aromatic planes, no matter whether the planes belonged to individual molecules forming PAH crystallites, oligomeric aggregates, or PAH/oligomer aggregates. Conclusions refer to the chemical structure of the optical isotropy phase occurring in carbonaceous materials, electrical conductivity of the materials, and X-ray measurements of the average size of the aromatic units (La).