INELASTIC NEUTRON-SCATTERING STUDY OF METHYL TUNNELING IN AN ORIENTEDSINGLE-CRYSTAL OF 2,6-DIMETHYLPYRAZINE AT LOW-TEMPERATURE AND ROTATIONAL-POTENTIAL CALCULATIONS

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