The Data Center on Atomic Transition Probabilities at the U.S. National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards (NBS), has critically evaluated and compiled atomic transition probability data since 1962 and has published tables containing data for about 39,000 transitions of the 28 lightest elements, hydrogen through nickel. In these tables, all stages of ionization are covered for which data are available, and forbidden transitions are included. Additional data for many heavy elements are critically compiled in the Handbook of Chemistry and Physics (CRC Press). The compilations for elements Z=1-28 contain accuracy estimates for each transition probability listed and are generally limited to reference data, I.e., data estimated to have uncertainties of less than 50%. This material is also part of a large spectroscopic database on the Internet, the NIST Atomic Spectra Database at the URL address http://physics.nist.gov/asd
. This address also contains a link to a comprehensive bibliographic database on atomic transition probabilities from 1914 to the present, maintained by NIST.