COVALENCY OF BONDING IN BETA-SN

The almost-forbidden reflection (202) in -Sn has been measured on a single crystal at 300 K using Mo K radiation. Careful checks for the absence of multiple Bragg scattering were made. The intensity data correspond to the experimental value F(202)=0.260.05 of the structure factor. The experimental value includes contributions from both the antisymmetric-bond-charge distribution and the antisymmetric anharmonic core motion, which are found to be of opposite sign. Combination of the present result and a recent x-ray study of the anharmonicity yielded the value Fb(202)=0.390.08 for the contribution from antisymmetric-bond-charge distribution. A single parameter representation of the charge density is given and the present results are discussed in relation to those of a recent study on -Sn. © 1979 The American Physical Society.