Rotational Excitations and Tunnelling of Non-Equivalent Methyl Groups in Pb(CH3)4

Abstract

Rotational tunnelling and librations of the methyl groups in tetramethyllead have been measured as a function of temperature by inelastic neutron scattering. Tunnel splittings of 74 μeV and 30.7 (ieV and librational peaks at 3.6 μeV and 10.2 μeV have been observed. The data show that Pb(CH3)4 is isomorphous to Sn(CH3)4 with a space group Pa3, Z = 8 and the molecules at c-sites. Rotational potentials for both types of inequivalent CH3 groups are derived and used for the explanation of NMR-T1 measurements.