Knowledge Bank

The polarized absorption spectra of single crystals of tetraphenyl lead, tin, germanium, and silicon have been examined at $4.2\circ K$. The $0-0$ bands were split into several components separated by about $3cm-1$, and this splitting has been assigned as arising from intra-molecular exchange splitting. The energy of the $0-0$ band was found to increase as the size of the central atom increased. High field Zeeman experiments indicate that two spin-orbit routes predominate. Preliminary examination of the phosphorescence indicates that the emission may originate from two of the intramolecular exchange states.