Inelastic neutron scattering study of methyl tunnelling in an oriented single-crystal of 2,6-dimethylpyrazine at low temperature and rotational-potential calculations

Inelastic neutron scattering (INS) on an oriented single-crystal is used to assign directly the tunnelling splittings to the two crystallographically-inequivalent methyl groups in 2,6-dimethylpyrazine (C6N2H8) at 2 K. Their antiparallel conformation found by crystallography and their respective rotational barriers are reproduced by a combination of ab-initio and molecular mechanics calculations. These results are used for a better understanding of the methyl groups dynamics. (C) 1998 Elsevier Science B.V.