J. Plasma Fusion Res. SERIES, Vol.7 (2006) 327-330

Critical Compilation of Wavelengths and Energy Levels
for Atoms and Atomic Ions
READER Joseph
National Institute of Standards and Technology, Gaithersburg, MD 20899, USA（Received: 5 Octorber 2004 / Accepted: 20 May 2005）

Abstract
Current projects to critically compile wavelengths and energy levels for atoms and atomic ions at theNational Institute of Standards and Technology are summarized.
Keywords:
atom, atomic ion, energy level, ionization energy, percentage composition, transition probability,
wavelength
1．Introduction
At the National Institute of Standards and Technology (NIST) we are carrying out a systematic programof critical compilation of wavelengths and energy levels of atoms and atomic ions. The spectra to be compiled are selected according to their general importanceto science and industry. For example, spectra of tungsten are expected to be important for diagnosing plasmas in next generation tokamak devices. Hence, we are
now compiling the spectra and energy levels for W in all
stages of ionization [1]. Similarly, the spectra of neon
and argon are important for understanding many stellar objects as well as for diagnosing tokamak plasmas
and we are thus in the process of compiling the spectra of all Ne and Ar ions, including the neutral atoms.
The spectra of xenon are currently of great interest forplanned extreme ultraviolet microlithography; we havejust completed a comprehensive compilation of Xe inall stages of ionization.
For the most part, the data are experimental values
based on laboratory observations. In some cases, suchas for H-like and He-like ions, the data are derived from
calculations with sophisticated atomic structure codesthat include relativistic and quantum electrodynamic effects.
The process of producing a critical compilation requires the retrieval of all data from the literature for aparticular ion. In many cases this may require that data
be extracted from more than one paper. For neutral andsingly-ionized atoms it is not uncommon for 10 or more
papers to be used. Often the data from diﬀerent papers
are inconsistent and possibly contradictory. Where possible, we attempt to resolve these conflicts by use of
isoelectronic comparisons and ab initio calculations. In

some cases level identifications given in the literature
are incomplete in their specifications, and new calculations are needed to obtain appropriate names. If available, we tabulate the percentage compositions for theobserved levels. In many cases these compositions aretaken from our own calculations.
When data from two or more papers are blended together to form a single list of lines and levels, it is usually necessary to derive a new set of levels and to optimize their values so that the diﬀerences of the levelvalues (Ritz values) best reproduce the observed spectrum. This is usually done with a computer code [2] thatweights the wave numbers according to their uncertainties and minimizes the diﬀerences between the observed
wave numbers and those derived from the levels in an
iterative procedure. The final Ritz wavelengths are generally more accurate than those that were observed.
Finally, it is often necessary for us to determine an
ionization energy from the observed data. The accompanying paper [1] in this Conference by A.E. Kramida
describes one method that we have developed for thispurpose as well as other aspects of the compilation process. It also describes a new computer code for optimizing the energy level values.
In Fig. 1 we illustrate schematically the process ofcritically compiling wavelength and energy level data.
As can be seen, our independent calculations play animportant role in nearly all aspects of the process. The
example is for a case where three literature sources arebeing consulted. Although in practice there may be onlya single source that is needed, in many cases there may
be many more that have to be blended together to form
C 2006 by The Japan Society of Plasma

Science and Nuclear Fusion Research
Corresponding author’s e-mail: joseph.reader@nist.gov327

Critical Compilation of Wavelengths and Energy Levels for Atoms and Atomic Ions

Fig. 1 Process of critical compilation of wavelength and energy level data.

the final compilation.

2.2 E.B. Saloman and C.J. Sansonetti, Wavelengths,
Energy Level Classifications and Energy Levels for

2．Current critical compilations of spectral
lines and energy levels at NIST
We summarize our current projects:

the Spectrum of Neutral Neon, J. Phys. Chem. Ref.
Data in press (2004).

We have prepared a comprehensive critically evaluated compilation of the most accurate wavelength measurements for classified lines of neutral neon (Ne I) in
its natural isotopic abundance. Data from 19 sources
spanning the region 256 Å to 54 931 Å are included.
Based on this line list we have derived optimized values
for the energy levels of neutral neon. Tabular data for
1595 classified lines and 374 energy levels are provided.
In addition to the observed wavelengths, we present revised wavelengths calculated from the optimized energy levels for all lines that have been previously recommended for use as secondary wavelength standards.

2.1 E.B. Saloman, Energy Levels and Observed
Spectral Lines of Xenon, Xe I through Xe LIV, J.
Phys. Chem. Ref. Data 33, 765-921 (2004).

The energy levels and observed spectral lines of thexenon atom, in all stages of ionization for which experimental data are available, have been compiled. Suﬃcient data were found to generate level and line tables
for Xe I-Xe XI, Xe XIX, Xe XXV-Xe XXIX, Xe XLIIIXe XLV and Xe LI-Xe LIV. For Xe LIII and Xe LIV
theoretical values are compiled for the energy levels. In
15 of the other stages a few lines are reported. Experimental g-factors are included for Xe I, Xe II and Xe III.
A value, either experimental, semiempirical, or theoretical, is included for the ionization energy of each ion.

2.3 A.E. Kramida, Critical Compilation of the Wavelengths and Energy Levels of Singly Ionized Beryllium (Be II), Physica Scripta in press (2004).

Energy levels and wavelengths of the second spectrum of beryllium (Be II) were critically compiled. Energies of the levels involving excitation of the valence
electron were re-optimized using the new data on tran-328

Critical Compilation of Wavelengths and Energy Levels for Atoms and Atomic Ions

sition wavelengths or calculated using precise semiempirical formulas. Energies of the doubly- and triplyexcited terms were taken from a recently publishedcompilation [A.E. Kramida, Physica Scripta 57, 66(1998)] or obtained from recently published Auger electron spectra. Observed wavelengths and wavelengths
calculated from the diﬀerences of the upper and lower
levels are given together with their uncertainties.

2.7 J.E. Sansonetti, Wavelengths, Transition Probabilities and Energy Levels for the Spectra of Rubidium (Rb I through Rb XXXVII), J. Phys. Chem.
Ref. Data to be submitted.

Energy levels, with designations and uncertainties,
have been compiled for the spectra of the neutral atom
and all positive ions of rubidium (Z = 37). Wavelengths
with classifications, intensities, and transition probabilities are also tabulated. In addition, ground statesand ionization energies are listed. For most ionization
stages experimental data are available; however for ionization stages where only theoretical calculations or fitted values exist, these are reported. There are a few
ionization stages for which only a calculated ionizationenergy is available.

2.4 A.E. Kramida, Critical Compilation of Wavelengths, Energy Levels and Transition Probabilities for W I and W II, J. Phys. Chem. Ref. Data
submitted (2004).

Energy levels, wavelengths and transition probabilities of the first and second spectra of tungsten, W I andW II, have been compiled. Wavelengths of observed
transitions and energy levels derived from those wavelengths have been obtained from a critical evaluationof the available literature. Measured transition probabilities for some of the observed transitions have been
compiled from the published literature.

2.8 A.E. Kramida and G. Nave, Optimized energy
levels, level naming, new FTS measurements andcompiled spectral lines of Ne II, Eur. Phys. J. D to
be submitted.

Spectra of neon-filled hollow cathode discharge
lamps were observed by means of high-resolution
Fourier-transform spectroscopy (FTS) covering the region from vacuum ultraviolet to near infrared. Combining these new measurements with results of other FTS
and conventional-spectroscopy observations, we compiled a complete list of approximately 1700 spectral
lines of Ne II covering the range from 324 Å to 13 µm.
All known energy levels of Ne II were derived from thisline list with improved accuracy. The newly optimizedenergy levels were used to derive a set of Ritz wavelength standards in the vacuum ultraviolet that are ingood agreement with previously used data. With thehelp of parametric calculations, an improved classification of energy levels was made and the existing controversy in the naming of strongly mixed levels was resolved.

2.5 J.J. Curry, A Critical Compilation of Wavelengths, Energy Levels and Transition Probabilities for Ba I and II, J. Phys. Chem. Ref. Data 33,
725-746 (2004).

Energy levels, wavelengths, and transition probabilities for the first and second spectra of barium, Ba I
and Ba II, have been compiled. Wavelengths of observed transitions and energy levels derived from thosewavelengths have been obtained from a critical evaluation of the available literature. Measured and calculatedtransition probabilities for some of the observed transitions have been obtained from the recent compilation ofKlose, Fuhr and Wiese (J. Phys. Chem. Ref. Data 31,217 (2002)).
2.6 W.Whaling, W.H. C. Anderson, M.T. Carle, J.W.
Brault and H.A. Zarem, Argon I Lines Produced

2.9 A.E. Kramida and G. Nave, New FTS measure-in a Hollow Cathode Source, 332 nm -5865 nm,ments, optimized energy levels and refined VUVJ. Res. Natl. Inst. Stand. Technol. 107, 149-169

standards in the Ne III spectrum, Eur. Phys. J.

(2002).

D to be submitted.

We report precision measurements by Fourier transform spectroscopy of the vacuum wave number, line
width and relative signal strength of 928 lines in theAr I spectrum. Wavelength in air and classification ofthe transition are supplied for each line. A comparisonof our results with other precision measurements illustrates the sensitivity of Ar I wavelengths to conditionsin the light source.

All observed spectral lines of Ne III in the range
204 Å to 36 µm have been compiled and critically evaluated. Fifty seven visible and ultraviolet lines of Ne III
have been precisely measured using Fourier transform
spectroscopy. An optimized level scheme has been derived from the total list of observed lines. Relative positions of about 180 out of a total of 226 previously
known energy levels of Ne III have been determinedwith improved accuracy compared to previous studies.
Excitation energies of almost all levels have been re329

Critical Compilation of Wavelengths and Energy Levels for Atoms and Atomic Ions

vised by 1.5 to 2.0 cm−1 . More than 100 precise wavelength standards in the region 210 to 2900 Å with welldefined uncertainties have been derived. Concepts oferror current and covariance matrix have been implemented in a computational algorithm that permits one
to derive the uncertainties of Ritz wavelength standards
obtained from a set of least-squares-optimized energy
levels. Nine new energy levels have been found and16 new transitions have been identified in the extreme
ultraviolet region. The ionization potential has been increased by 4.5 cm−1 . The new value is 511543.5 ± 2.7
cm−1 (63.4233 ± 0.0003 eV).

5. Wavelengths and energy levels for Ar in all stages ofionization (C.J. Sansonetti and T. Shirai).
6. Wavelengths and energy levels for W III-W LXXVI(T. Shirai and A.E. Kramida).
7. Wavelengths, energy levels, and transition probabilities for Cs in all stages of ionization (J.E. Sansonetti).
8. Wavelengths and energy levels for Ne VII and Ne
VIII (A.E. Kramida).
This work is supported in part by the Oﬃce of Fusion
Energy Sciences of the U.S. Department of Energy andby the U.S. National Aeronautics and Space Administration.

3．Compilations in progress at NISTThe following compilations are currently inprogress:
1. Wavelengths and energy levels for Kr in all stages ofionization (E.B. Saloman).
2. Wavelengths and energy levels for Ga in all stages ofionization (T. Shirai, J. Reader, A.E. Kramida and J.
Sugar).
3. Wavelengths and energy levels for Sr in all stages ofionization (G. Nave).
4. Wavelengths and energy levels for Ba III- Ba LVI(J.J. Curry).

[1]
[2]

330

References
A.E. Kramida, paper P2-61, this Conference.
For this purpose, we often use the program
ELCALC, written by L.J. Radziemski (The Research Corporation, Tucson, Arizona, 85712,U.S.A.) The procedure and definition of levelvalue uncertainties are described in L.J. Radziemski, Jr. and V. Kaufman, J. Opt. Soc. Am. 59, 424(1969). A more advanced code for this purpose,LOPT, has been written by A.E. Kramida, see reference [1].