The vibrational spectra of tetragonal and orthorhombic PbO

The i.r. and Raman spectra of tetragonal (red) and PbO and orthorhombic (yellow) PbO have been obtained. Frequencies, in good agreement with those observed, have been calculated using the Wilson FG matrix method. In both forms of PbO, it was found necessary to include metal-metal interactions in order to obtain such agreement. The absence of coincidences between the i.r. and Raman spectra of yellow PbO support the conclusion, reached by neutron deffraction studies, that, the space group of yellow PbO is the centrosymmetric D 2 h 11 ( Pbcm ); thus this material cannot be ferroelectric, as has previously been suggested.