ABSTRACT
The analysis of diatomic spectra was solved in principle by Heurlinger in 1916-20. The next half decade, the final years of the old quantum theory, was a period of consolidation and experimental advances, a time in which spectra of first row diatomics were studied, cataloged, and brought to a semblance of order. Electronic manifolds were built stepwise from transitions known to have a state in common, fitted by trial and error to an energy scale. Fortunately, molecules with the same number of electrons had broadly similar manifolds.
