Fermium energy level diagram

Energy levels and transitions of neutral fermium (Fm I): 8 levels and 7 classified lines below 2 µm taken from the cited literature, each line with its vacuum wavelength and frequency and, for 7 of them, the reduced dipole matrix element. The NIST Atomic Spectra Database lists only the ground level and the ionisation limit of fermium, so the level energies on this page are those of the literature sources named below.

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

Key transitions of fermium

λ, ν from the level energies of the cited literature (NIST lists no excited levels) unless a measured frequency for this isotope is available. A: measured value or NIST. Γ/2π: natural linewidth of the upper level, 1/(2πτ).

²⁵⁵Fm hyperfine structure (I = 7/2)

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

Isotope shifts

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

Closed and nearly closed transitions of fermium

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 Fm 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, or a model calculation.

Fm energy levels

Fm⁺ ionisation limit 52400.00 cm⁻¹ = 6.49677 eV (190.840 nm)

Sources

• Allehabi, Li, Dzuba, Flambaum, 'Theoretical study of electronic structure of erbium and f…
• Backe, Dretzke, Fritzsche, Haire, Kunz, Lauth, Sewtz, Trautmann, Hyperfine Interact. 162,…
• Sewtz, 'Optische Spektroskopie an Fermium (Z=100)', doctoral thesis, Johannes Gutenberg-U…
• Urquiza-Gonzalez, Stemmler, Albrecht, Bally, Bender, et al., 'High-Resolution Laser Spect…
• Urquiza-Gonzalez, Stemmler, Albrecht, Bally, Bender, et al., 'High-Resolution Laser Spect…

NIST lists only the ground level and a bracketed (extrapolated) limit. Seven odd levels are known, all found by resonance ionization of 255Fm from the ground state: two near 398 nm (R1, R2; energies, J and hyperfine constants from the 2026 high-resolution work, entered as measured) and five between 365 and 352 nm (2005, second-hand, +-1.5 cm^-1, J from theory). A_s of the two 398 nm lines are partial rates from saturation measurements (model-dependent); A_s of the other five lines and all g_J are calculated values marked theory; A_s_lower_bound holds the two measured lower limits. No lifetime is stored. Isotope shifts are nu(first) - nu(second), reference 250Fm, on the R2 line. Hyperfine constants were printed in GHz and converted to MHz. Term labels of the excited levels are leading components of calculated wavefunctions (proposals). The broad structure at 25 740(5) cm^-1 seen in 2003 (about 30 cm^-1 wide, possibly a two-photon resonance) is not entered as a level. CLAUDE.md of the project records an earlier owner decision not to add Fm; this file was written at the request of the 2026-10-02 workflow task and changes nothing else.

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