Floppy structure of the benzene dimer: <i>Ab</i> <i>initio</i> calculation on the structure and dipole moment

Abstract

The structure of the benzene dimer has aroused considerable interest due to recent experimental measurements and hence extensive theoretical calculation is topical. Nine structures of the benzene dimer were investigated using the second-order Mo/ller–Plesset theory. The calculations were performed with smaller (MIDI-1+s+p) and larger (6-31+G*) basis sets. The T-shape structure was found to be the most stable but with a very shallow minimum; the wagging motion around the lowest hydrogen in the range of ±10° is practically nonhindered. These results together are consistent with the structure found experimentally. The final binding energy for the T structure (distance of molecular centers equal to 5.0 A) is −2.7±0.4 kcal/mol, which is more than the value derived from experiments. The calculated dipole moment is in excellent agreement with experiment.