Excerpt from Atomic Energy Levels as Derived From the Analyses of Optical Spectra, Vol. 3: The Spectra of Molybdenum, Technetium, Ruthenium, Rhodium, Palladium, Silver, Cadmium, Indium, Tin, Antimony, Tellurium, Iodine, Xenon, Cesium, Barium, Lanthanum-Hafnium, Tantalum, Tungsten, Rhenium, Osmium, Iridium, Platinum, Gold, Mercury, Thallium

The present Volume, including data to December 1957, is the third of a series being prepared at the National Bureau of Standards under a project on the compilation of atomic energy levels derived from the analyses of Optical spectra.

Volume I, published in June 1949, contains the energy levels Of 206 spectra of the elements Hydrogen through Vanadium, Z 1 through 23. Volume II, completed in August 1952, includes similar data for 152 spectra of the elements Chromium through Niobium, Z: 24 through 41. Volume III covers the elements Molybdenum through Lanthanum, Z =42 through 57; and Hafnium through Actinium, Z=72 through 89. It includes 124 spectra, and is identical in arrangement with Volumes I and II. The form of presentation is that recommended by the majority of interested scientists who received a questionnaire proposed by the National Research Council Committee on Line Spectra of the Elements, when the program was started in 1946.

The manuscript has been prepared by Charlotte E. Moore under the direction of William F. Meggers, Chief of the Spectroscopy Section of the Atomic and Radiation Physics Division. The success of this project has depended heavily upon the cordial and continuing collaboration of the many spectroscopists who have made an unusual effort to furnish data in advance of publication. Their efforts together with the unfailing cooperation of the National Research Council Committee are greatly appreciated.

Perhaps the most difficult phase of this extensive program lies ahead. The two groups Of rare-earth spectra (58 Cerium through 71 Lutetium, and 90 Thorium through 100 Fermium) remain for Volume IV. At best, the preparation of this Volume within the next few years will tax the most experienced and talented workers available. These spectra are the most intricate and least known Of atomic spectra. Consequently the type of collaboration we have enjoyed with qualified spectroscopists in the preparation of the first three Volumes Of the Atomic Energy Levels series will have not only to continue but be substantially augmented if the fourth Volume is to be brought to satisfactory fruition.

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