Iron energy level diagram

Energy levels and transitions of neutral iron (Fe I): the 71 strongest classified lines below 2 µm from the NIST Atomic Spectra Database and the 47 levels they connect, each line with its vacuum wavelength, frequency and, for 71 of them, the reduced dipole matrix element derived from the NIST transition rate. Measured lifetimes, transition rates, hyperfine constants and isotope shifts from the literature are included, each with its citation.

Hover a line or a level to isolate it, click to keep it selected. Scroll to zoom, drag to move.

Download: diagram (PDF) diagram (SVG) transitions (CSV) levels (CSV) source code

Key transitions of iron

λ, ν from NIST level energies unless a measured frequency for this isotope is available. A: measured value or NIST. Γ/2π: natural linewidth of the upper level, 1/(2πτ).

⁵⁷Fe hyperfine structure (I = 1/2)

Measured A, B constants; sources in the data file.

Isotope shifts

Shift = ν(first isotope) − ν(second isotope).

Closed and nearly closed transitions of iron

A transition is closed when its upper level can decay only to the level it was excited from, so the atom keeps scattering photons. “closed”: among the levels NIST lists, no other level below the upper level has the opposite parity and |ΔJ| ≤ 1, so no other electric-dipole decay exists. Otherwise the leak is the sum of the branching ratios of the other decay lines of the upper level (or 1 − branching ratio where that of the line itself has been measured), and the number of photons is 1 / leak. “≥” and “≤”: at least one possible decay path has no listed rate, so the leak is a lower limit. These numbers are derived from the branching ratios, lifetimes and rates of this page, not measured as such; the tag names the weakest of the inputs, * marks theory and ≈ a model or semi-empirical calculation. Listed: lines that start on the ground level or on a metastable level and leak at most 10 %, unless more than three possible decay paths have no listed rate. Fine-structure levels only: hyperfine and Zeeman dark states and forbidden decays without a listed rate are not considered. Select a line in the diagram for the full list of its leak channels.

Listed Fe transitions below 2 µm

Reduced dipole matrix elements follow the convention A = ω³|d|²/(3πε₀ħc³(2J′+1)), with J′ the upper level. Tags show where a number comes from: measured, NIST compilation, high-accuracy theory, a semi-empirical calculation (Kurucz line list, used only where no measurement or NIST value exists; typically within a factor 2), or a model calculation.

Fe energy levels

Fe⁺ ionisation limit 63737.70 cm⁻¹ = 7.90247 eV (156.893 nm)

Sources

• Belmonte, Pickering, Ruffoni, Den Hartog, Lawler, Guzman, Heiter, Astrophys. J. 848, 125 …
• Belmonte, Pickering, Ruffoni, Den Hartog, Lawler, Guzman, Heiter, Astrophys. J. 848, 125 …
• Childs & Goodman, Phys. Rev. 148, 74 (1966), quoted in Krins, Oppel, Huet, von Zanthier, …
• Dembczynski et al., Z. Phys. A 294, 313 (1980), quoted in Huet, Pettens, Bastin, 'Isotope…
• Huet, Pettens, Bastin, 'Isotope shifts and hyperfine structure of the laser-cooling Fe I …
• Krins, Oppel, Huet, von Zanthier, Bastin, Phys. Rev. A 80, 062508 (2009), Table II
• Kurucz, R. L., Can. J. Phys. 89, 417 (2011); semi-empirical line list gf2600.pos of 2017-…
• NIST ASD
• NIST ASD level energies
• O'Brian, Wickliffe, Lawler, Whaling, Brault, J. Opt. Soc. Am. B 8, 1185 (1991), Table 1 (…
• O'Brian, Wickliffe, Lawler, Whaling, Brault, J. Opt. Soc. Am. B 8, 1185 (1991), Table 1 (…
• O'Brian, Wickliffe, Lawler, Whaling, Brault, J. Opt. Soc. Am. B 8, 1185 (1991), Table 1 (…
• O'Brian, Wickliffe, Lawler, Whaling, Brault, J. Opt. Soc. Am. B 8, 1185 (1991), Table 1 (…
• O'Brian, Wickliffe, Lawler, Whaling, Brault, J. Opt. Soc. Am. B 8, 1185 (1991), Table 1 (…
• O'Brian, Wickliffe, Lawler, Whaling, Brault, J. Opt. Soc. Am. B 8, 1185 (1991), Table 1 (…
• O'Brian, Wickliffe, Lawler, Whaling, Brault, J. Opt. Soc. Am. B 8, 1185 (1991), Table 1 (…
• O'Brian, Wickliffe, Lawler, Whaling, Brault, J. Opt. Soc. Am. B 8, 1185 (1991), Table 1 (…
• O'Brian, Wickliffe, Lawler, Whaling, Brault, J. Opt. Soc. Am. B 8, 1185 (1991), Table 1 (…

Isotope shifts are nu(first)-nu(second) as in the source (delta nu_{56,54} = nu56 - nu54). 57Fe has I=1/2 so only A constants exist. O'Brian 1991 Table 1 was read from the scanned PDF (text layer checked against the page image). Lifetime uncertainties for O'Brian/Belmonte are the papers' blanket 'larger of 5 % or 0.2 ns'. rme_J_ea0 values are derived from measured A (S = A g_upper lambda_vac^3 / 2.0261e18, lambda in Angstrom). WebSearch was unavailable in this session (budget exhausted); sources were located through DOI/bibliographic lookups (Crossref, OpenAlex), VizieR, ADS and arXiv.

Atoms with measured data

• Lithium-632 levels, 85 lines
• Lithium-732 levels, 85 lines
• Beryllium-917 levels, 26 lines
• Sodium-2336 levels, 106 lines
• Magnesium-2418 levels, 61 lines
• Magnesium-2518 levels, 61 lines
• Potassium-3934 levels, 84 lines
• Potassium-4034 levels, 84 lines
• Potassium-4134 levels, 84 lines
• Calcium-4035 levels, 61 lines
• Calcium-4335 levels, 61 lines
• Chromium-5256 levels, 87 lines
• Chromium-5356 levels, 87 lines
• Rubidium-8536 levels, 94 lines
• Rubidium-8736 levels, 94 lines
• Strontium-8440 levels, 70 lines
• Strontium-8640 levels, 70 lines
• Strontium-8740 levels, 70 lines
• Strontium-8840 levels, 70 lines
• Cadmium-11115 levels, 21 lines
• Cadmium-11315 levels, 21 lines
• Cadmium-11415 levels, 21 lines
• Caesium-13331 levels, 79 lines
• Barium-13744 levels, 89 lines
• Barium-13844 levels, 89 lines
• Dysprosium-16139 levels, 55 lines
• Dysprosium-16239 levels, 55 lines
• Dysprosium-16339 levels, 55 lines
• Dysprosium-16439 levels, 55 lines
• Erbium-16673 levels, 90 lines
• Erbium-16773 levels, 90 lines
• Erbium-16873 levels, 90 lines
• Thulium-16972 levels, 73 lines
• Ytterbium-17118 levels, 26 lines
• Ytterbium-17318 levels, 26 lines
• Ytterbium-17418 levels, 26 lines
• Mercury-19927 levels, 47 lines
• Mercury-20127 levels, 47 lines
• Mercury-20227 levels, 47 lines

All elements: periodic table