The benzene dimer, as a prototype of bonding between nonpolar molecules, has received much attention both from experimentalists and theorists. Theorists have been challenged by the subtle binding energy difference between two equilibrium structures of the benzene dimer, a T-shaped one and a slipped-parallel one. Its potential energy surface has 288 equivalent tilted T-shaped minima and 144 equivalent (less deep) slipped-parallel minima; the permutation-inversion symmetry group is G576. Internal rotations have very low barriers in some directions, but are strongly hindered in others. With the use of a global intermolecular potential energy surface from ab initio SAPT(DFT) calculations, we computed converged vibration-rotation-tunneling levels and properties of the benzene dimer for all 54 irreducible representations of the group G576. The calculations tell us which tunneling processes actually occur; they predict the corresponding level splittings and frequencies of the intermolecular vibrations that can be directly compared with (future) experimental spectra.

Rovibrational and tunneling states of the benzene dimer: An ab initio study

239th National Meeting (2010)

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