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The ionization energies in the table are based on a recent survey of the literature. A reference to one or another data compilation is given for a number of elements; the cited compilation gives the reference(s) for the original ionization-energy data. The uncertainties are mainly in the range from less than one to several units in the last decimal place, but a few of the values may be in error by 20 or more units in the final place; i.e., the error of some of the two place values could be greater than 0.2 eV. Estimated uncertainties of the ionization energies are usually given in the references. Although no more than four decimal places are given, the accuracies of some of the better known values would, in eV units, be limited only by the uncertainty in the conversion factor, 1.239 842 44(37) × 10-4 eV/cm-1.

The ground-state electron configurations of elements heavier than neon are shortened in the table by using rare-gas element symbols in brackets to represent the corresponding electrons. The ground levels of all neutral atoms have reasonably meaningful LS-coupling names, the corresponding eigenvector percentages lying in the range from ~55% to 100%.  These names are listed in the table, except for Pa, U, and Np; the lowest few ground-configuration levels of these atoms comprise better 5N(L1S1J1), 6dj7s2 (J1 j) terms than LS-coupling terms. The relatively large spin-orbit interaction of the 6p electrons produces jj-coupling structures for the (6p21/2)0, (6p21/26p3/2)o3/2, and (6p21/26p23/2)2 ground levels of the 6p2, 6p3, and 6p4 configurations of neutral Pb, Bi, and Po, respectively. These jj-coupling names are more appropriate for these atoms than the alternative LS-coupling designations in the table.

In Version 5 of the Atomic Spectra Database, a new Web interface for retrieval of ionization energies and total binding energies of ground states of all atomic spectra was added.  This site now links to the Atomic Spectra Database.

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NIST Standard Reference Database 111
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Online: April 1998  -  Last update: September 2013

Alexander Kramida
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