We present an application of rotational tunneling spectroscopy to quantitatively probe interactions in a host-guest system. In particular, the methyl rotational tunneling spectrum of p-xylene confined in nanoporous zeolite crystals has been measured by high resolution inelastic neutron scattering. We interpret the tunneling spectra as a combination of transitions involving two coupled methyl rotors as well as a transition involving one of the two remaining independent rotors, in a manner consistent with the observed spectral energies and intensities. The extracted framework-methyl and methyl-methyl potential energy parameters are presented and discussed.
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