Molecular Structure and Phase-shift of Tetramethyllead as Studied by Gas Electron Diffraction

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Abstract
The molecular structure of tetramethyllead has been determined by the sector-microphotometer method of gas-phase electron diffraction. The structure parameters determined by a least-squares analysis on molecular intensities are, with estimated limits of error, as follows; rg(Pb–C)=2.238±0.009 Å, rg(Pb–H)=2.72±0.06 Å, rg(C···C)=3.66±0.07 Å, and rg(C–H)=1.08±0.02 Å. The experimental cut-off point was nearly 37 in q value for the 42.0 keV electrons; this was not in sufficient agreement with the theoretical value as calculated from the Thomas-Fermi-Dirac potential for Pb and from the Hartree-Fock potential for C. Moreover, the experimental background showed a significant deviation from its theoretical counterpart in the region of small q values. This discrepancy has not been accounted for even by the use of scattering factors based on a relativistic SCF calculation, or by the correction for the polarization effect available at present.