Coherent internal and centre of mass quantum rotation of methyl groups in the p-tert-butyl-calix[4]arene(2:1)p-xylene supramolecular complex

The low-temperature inelastic neutron scattering spectrum measured for the p-tertbutylcalix[ 4]arene(2:1)p-xylene complex has been interpreted in the framework of a quantum dynamical model assuming a rotational motion of the p-xylene CH3 groups correlated to the translational motion of their centre of mass. By comparing the experimental data with calculated energies and intensities, the effective anharmonic and anisotropic molecular potential experienced by the methyl groups has been derived. The wavefunctions deduced from the spectroscopy results are used to calculate the proton density distribution in the plane of the motion.