Pseudo Jahn-Teller effect in stacked benzene molecules

Chemically bound structures of several benzene molecules are studied both analytically and numerically. The bonds in these structures are established by replacing the intra pi-bonds of C-6 rings by the inter sigma-bonds. The rearrangements of different pi-bonds may take place differently which causes distortions of C-6 rings. The reason of the distortions is the pseudo-Jahn-Teller effect (PJTE). In the case of two chemically bound benzene molecules in a hollow position (with direct on-top stacking), called as bi-benzene, three different distorted states in addition to the undistorted one are found to exist. PJTE leads also to a chemical bonding of three and more benzene molecules stacked directly on-top of each other. These bound structures do not exist for undistorted molecules. All bound states, although being metastable are separated from the unbound ones by energy barriers greater than or similar to 2 eV. It is found that the height of the barrier for symmetric bi-benzene is essentially affected by the Jahn-Teller effect. (C) 2015 Elsevier B.V. All rights reserved.