Methyl rotational tunneling dynamics of p-xylene confined in a crystalline zeolite host

The methyl rotational tunneling spectrum of p-xylene confined in a crystalline nanoporous zeolite host was analyzed that can be explained by a combination of single-rotor and coupled-rotor tunnelings. The number and relative intensities of the tunneling peaks observed by inelastic neutron scattering (INS) indicated the presence of methyl-methyl coupling interactions in addition to the methyl-zeolite interactions. The tunneling spectra based on INS measurements was assigned to three of the four inequivalent methyl rotors in the crystal structure of the material. The crystal structure and the absence of additional peaks in the INS spectra suggest that the tunneling of the fourth inequivalent rotor is hindered and inaccessible to INS measurements.