The spectrum of PbO has been photographed in absorption. A new system, designated as the $E$ system, has been found. It is nearly coincident with the $D$ system. A number of previously unclassified bands together with some new bands are assigned to a new system, replacing Mecke's $C$ system. The $D$ system has been extended and the new values require that $x_e{{\omega }_e}^{\prime }$ be changed from 1.05 to 3.13. All three systems have the same lower level in common with the $A$ and $B$ systems.

• Received 16 January 1935

DOI:https://doi.org/10.1103/PhysRev.47.377