Rotational Tunnelling in Methyl Metal Compounds X2(CH3)4 with X = As, Sb, Bi

Abstract

Abstract Rotational excitations of methyl groups attached to metal atoms of the fifth main group have been investigated in X2(CH3)4 crystals with X = As, Sb, Bi by 1H nuclear magnetic resonance (NMR) relaxation measurements and inelastic neutron scattering (INS). CH3 rotation has been found to be rather weakly hindered (activation energies between 1.7 kJ/mol and 5.8 kJ/mol) so that quantum effects are important to describe the results. Tunnel splittings between 0.1 μeV and 23 μeV have been observed. Non-equivalent methyl groups in tetramethyldistibane and tetramethyldibismuthane have been identified by both INS and NMR. A consistent description of the T1 data is possible by Haupt's equation. The rotational potentials could be derived and relations to the crystal structure have been discussed.