The N2-benzene tethered top

Ab initio calculations have been carried out for the weakly bound cluster of nitrogen and benzene and for the isoelectronic cluster of acetylene and benzene. With nitrogen and acetylene having quadrupole moments of opposite sign, their energetically preferred orientation with respect to benzene differs, with N2 parallel and acetylene perpendicular to the benzene plane. The interaction surface for the N2-benzene dimer reveals that there is little potential energy change for rotation of N2 about an axis perpendicular to the benzene plane and little change for considerable displacement away from its equilibrium position above the center of the benzene ring. Hence, this unique potential surface is suggestive of free rotation by N2 (a spinning top) along with significant ground vibrational state displacement across the surface of benzene leading to a symmetrically tethered N2.