Calculations of the geometry and binding energy of aromatic dimers: Benzene, toluene, and toluene–benzene

Abstract

Calculations of the geometries and energies of the benzene, toluene, and toluene–benzene dimers using a combination of atom–atom and multipolar potentials are presented and discussed. An exponential-six atom–atom potential plus a molecular quadrupole–quadrupole interaction term gives the reported parallel displaced C2h benzene dimer geometry. The excited state behavior of the benzene dimer can be qualitatively understood based on this calculation. The toluene–benzene dimer is well modeled by these terms in addition to a dipole–quadrupole interaction term. Both parallel displaced and perpendicular configurations are obtained in agreement with the experimental data. Using exponential-six dipole–dipole, quadrupole–quadrupole, and dipole–quadrupole interactions the toluene dimer can be satisfactorily modeled. The calculations generally suggest that excitation of parallel displaced dimers can lead to rearrangement (and possible excimer formation) in the excited state.