Structures and binding energies of benzene–methane and benzene–benzene complexes. An ab initio SCF/MP2 study

Abstract

Ab initio SCF/MP2 potentials are calculated on benzene–methane and benzene–benzene complexes. Although no energy stabilization appears at the Hartree–Fock level, a small but non-negligible stabilization in energy is observed at the MP2 level in both complexes, indicating the importance of the dispersion energy. Besides the dispersion energy, the electrostatic interaction plays some role in determining the relative stabilities in several cases. The most stable structure of the benzene–methane complex adopts a C_3v symmetry with methane lying on the benzene C₆ axis and one hydrogen atom pointing towards benzene. The binding energy of this structure is –1.95 kcal mol^–1 from MP2/MIDI-4** calculations and –1.09 kcal mol^–1 from MP2/6-31G** calculations, where a p-polarization function is added only on the H atoms of methane. The benzene–methane complex is much less stable than the benzene–benzene complex.