NIST: Atomic Spectra Database - Ground States and Ionization Energies Help File

The ASD database provides data on ground states and ionization energies for atoms and atomic ions. For more information consult Introduction to and Contents of the ASD.

Ground States and Ionization Energies (GSIE) Search Form

This search form, referred to as the GSIE Form, provides access to the ground state specifications, ionization energies, and total binding energies data. Submitting information provided by the user on the GSIE Form generates a list of GSIE data for specified spectra (elements and ionization stages).

At a minimum, the user must enter the spectra of interest (e.g., C I) and then click "Retrieve Data".

The GSIE Search Form prompts the user for the following information:

Spectra of interest (e.g., Fe or H-DS I).
Ionization or binding energy units (selected from the pulldown menu).
The energies may be displayed in one of the following units:
- cm⁻¹ (reciprocal centimeter or wavenumber)
- eV (electron Volt), the default unit
- Rydberg
- Hartree (=2×Rydberg)
- GHz
Choice of viewing the output as an HTML table or an ASCII table (selected from the pulldown menu).
Choice of energy ordering of the output, i.e., ordered by the nuclear charge Z (default) or by isoelectronic sequences.
Choice of the output information.

In particular, the user can choose to display the total binding energies instead of the ionization energies, which are selected by default.
Choice of the output of the relevant available bibliographic references.
For all GSIE data, bibliographic references are available and can be retrieved by selecting the "Bibliographic references" checkbox.

For GSIE output, the default is to display the following data:

Atomic number
Spectrum name
Ion charge
Isoelectronic sequence symbol
Ionization energy
Uncertainty
Ground-state electronic shells
Ground-state level label
Ionized configuration (i.e., configuration and level labels and the J value of the level of the next ion, to which the given ionization energy corresponds).
Bibliographic References

To suppress display of any of the information listed above, the corresponding checkbox can be unclicked.

Selecting Spectra for GSIE Searches

The Ground States and Ionization Energies (GSIE) Spectra input box works in exactly the same way as the Spectra input box in the Line Search.

Examples of most common Spectra for the GSIE Search

To specify	Enter
All neutral atoms	H-Ds I
All spectra of sodium	Na
Spectra of all elements between Ne and Fe in isoelectronic sequences between Ne-like and S-like	Ne-Fe Ne-like-S-like
Lithium-like magnesium	Mg x
Lithium-like magnesium	mg Li-like
Singly-ionized ¹¹B	11B II

Output for GSIE
(by table column heading)

Atomic Number: Number of protons in the atomic nucleus.
Spectrum Name: Standard spectroscopic notation, i.e., the element symbol followed by the Roman number of the spectrum (equal to the ion charge plus one).
Ion Charge: Electric charge of the atom or ion.
Element name: Standard name of the chemical element, according to NIST Periodic Table of the Elements
Isoelectronic sequence: Chemical symbol of the neutral atom having the same number of electrons as the given ion.
Ground Shells
Ground Configuration
Ground Level
Ionized Level
Ionization Energy: The minimum energy required to remove one electron from the atom or ion in its ground state.
Total Binding Energy: The minimum energy required to remove all electrons from the atom or ion in its ground state. It is calculated online by summing up all relevant ionization energies.
Uncertainty
Bibliographic References

Ground Shells

The ground shells designation is given in groups of symbols: an integer number corresponding to the principal quantum number of the shell, followed by the standard electronic shell symbol (e.g., s, p, d) with a superscript indicating the number of electrons the shell ("1" is omitted for brevity).

For complex atoms and ions with a large number of occupied electronic shells, certain groups of fully-occupied shells are designated with an element symbol corresponding to a neutral atom having these fully occupied shells in its ground state, given in square brackets before the list of outer shells. These shell groups are listed below:

[Ne] = 1s²2s²2p⁶,
[Ar] = 1s²2s²2p⁶3s²3p⁶,
[Kr] = 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶,
[Cd] = 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²,
[Xe] = 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p⁶,
[Hg] = 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p⁶4f¹⁴5d¹⁰6s²,
[Rn] = 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p⁶4f¹⁴5d¹⁰6s²6p⁶

Ground Configuration

In this column, ASD gives the electronic configuration for the largest component in the calculated eigenvector of the ground level. These largest components are determined by theoretical calculations involving various approximations. Thus, some uncertainties are involved, especially for complex heavy atoms or ions. Any ancestor terms or J values appropriate to this eigenvector component are normally included with the configuration, as in the examples in the Introduction to Atomic Spectroscopy.

See more about configuration designations in the Help for Levels sections and in the Introduction to Atomic Spectroscopy.

Ground Level

In this column, ASD gives the term symbol and J value for the largest component in the calculated eigenvector of the ground level. As with the configurations (see above), some uncertainties may be involved, especially for complex heavy atoms or ions.

Ionized Level

Designations given in this column include the configuration, term, and J value corresponding to the ground state of the next ion (i.e., the ion obtained by removing one electron from the given atom or ion).

Ionization Energy

This quantity is the minimum energy required to remove one electron from the atom or ion in its ground state. The ionization energies are stored in the database in units of cm⁻¹. Output in these units gives the most accurate values. Conversion to other units (eV or Rydberg) involves an additional uncertainty of the conversion factor. These factors, as well as their uncertainties, are taken from the latest CODATA recommended conversion factors. Before ASD version 5.5 of October 2017, uncertainties of these conversion factors were not taken into account in the displayed data. Starting with v.5.5, these uncertainties are combined in quadrature with the uncertainties of the stored data, and the output quantities are rounded off according to the combined uncertainties. Thus, the accuracy of the output energies is somewhat degraded when the units of eV or Rydberg are used.

Some ionization energies are in square brackets "[ ]" and some are in parentheses "( )". Square brackets indicate the energies determined by interpolation, extrapolation, or other semi-empirical procedure relying on some known experimental values. Parentheses indicate energies that have been determined from an ab-initio calculation, or are otherwise not derived from evaluated experimental data. Theoretical values are typically given for highly-ionized spectra, where experimental data are scarce. Theoretical data may also be given for hydrogen-like and helium-like spectra, where the accuracy of quantum-electrodynamic calculations often exceeds that of experimental observations.

Total Binding Energy

This quantity is the minimum energy required to remove all electrons from the atom or ion in its ground state. It is calculated online by summing up all relevant ionization energies. If the calculation involves some experimental or semi-empirical ionization energies, the value of the binding energy is treated as semiempirical and is enclosed in square brackets. If all the involved ionization energies are purely theoretical, the resulting binding energy is also considered to be theoretical and appears in the output enclosed in parentheses.

Uncertainty

Uncertainty of the ionization or binding energy value is given in a column next to the energy value, if it is available in ASD, provided that the corresponding checkbox is checked in the input form. If no explicit information about the uncertainty is available, it will be blank in the output. In such cases, the number of significant figures in the energy value gives an approximate estimate of the uncertainty. It is usually safe to assume that the probable error is between 2.5 and ~25 units in the last place. About 90 % of data in ASD satisfies this assumption. A better estimate of the uncertainty in a particular case may sometimes be obtained by consulting the original paper(s).

Note that, if the output is requested in the default units of eV or in the Rydberg units, the displayed uncertainties include the uncertainties of the corresponding conversion factors from the units of cm⁻¹. See more about this in the section for Ionization Energy.

For binding energies (determined as a sum of ionization energies of consecutive ionization stages), uncertainties are estimated from those of the ionization energies involved. Uncertainties of ionization energies taken from the same literature source are summed up linearly, assuming they are dominated by systematics. Uncertainties resulting from different sources are summed up in quadrature. If the uncertainty of an ionization energy involved in the summation is unknown, it is estimated as ten units of the least significant figure of the ionization energy.

Bibliographic References

For information on viewing the references, see the Locating references in the ASD Bibliography section of the "Help" file.