Atomic energy levels as derived from the analyses of optical spectra : the spectra of chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, arsenic, selenium, bromine, krypton, rubidium, strontium, yttrium, zirconium, and niobium / vol. 2. - Moore, Charlotte E. (Circular of the National Bureau of Standards ;, 1952)