Measured and calculated rotational tunnelling dynamics in methyl acetate

Abstract A low-field NMR and inelastic neutron scattering investigation of tunnelling methyl dynamics in methyl acetate has been performed. Tunnel frequencies of 1.3 μeV and 0.31 neV have been measured for the two chemically distinct methyl groups in the molecule. From the known crystal structure at 145 K, the observed quantum methyl dynamics can be reproduced from a time-independent, molecular mechanics calculation based on ab initio techniques and empirical atom–atom potentials. Although no spectral evidence of coupled methyl dynamics exists, the delocalisation and reorientation of the methyl groups at low temperature must be included in the calculation in view of the strong coupling potentials. This is achieved with a quantum mechanical mean-field approach.