Raman depolarization ratios and the symmetry of Si(NCO)4 and Ge(NCO)4

Depolarization ratios, ϱ, have been measured to determine whether or not these molecules are tetrahedral. Totally‐symmetric vibrations of Tb molecules have ϱ0, whereas for all lower symmetries ϱ may be anywhere between 0 and 0.75. For Si(NCO)4 there are two bands with ϱ0.65 and 0.64, showing clearly that it is not tetrahedral. For Ge(NCO)4 the results are ambiguous, for the highest value observed for a polarized line is 0.086. However there is other evidence against Td symmetry for this molecule, especially selection rule behaviour. It is concluded that neither molecule is tetrahedral. The true symmetry is not known. The complete Raman spectrum has been re‐measured, and the results are given.