Bond polarizability anisotropy: Resolution of the sign ambiguity

An internally consistent “valence–optical” scheme of additive bond and group polarizabilities, obtained from analysis of electric birefringence, refractivity and Raman intensity data, is shown to apply to a series of compounds of Group IVB elements. For all M‐halogen bonds considered (M = Si, Ge or Sn; halogen = C1, Br or I), only the positive option for ±γ, the bond anisotropy from Raman intensities, is compatible with the scheme. The negative alternatives for γ lead to results which are anomalous and in some instances not physically meaningful. This procedure permits a definitive resolution of the problem of the sign ambiguity in ±γ M‐halogen .