National, standard reference data series, NSRDS-NBS. 35. Atomic energy levels as derived from analyses of optical spectra; v. 2, Spectra of chromiun, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, arsenic, selenium, bromine, krypton, rubidium, strontium, yttrium, zirconium, and niobium [with lists of references]; by Charlotte E. Moore.