Chlorine energy level diagram

Energy levels and transitions of neutral chlorine (Cl I): the 79 strongest classified lines below 2 µm from the NIST Atomic Spectra Database and the 43 levels they connect, each line with its vacuum wavelength, frequency and, for 77 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 chlorine

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).

³⁵Cl hyperfine structure (I = 3/2)

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

Closed and nearly closed transitions of chlorine

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 Cl 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.

Cl energy levels

Cl⁺ ionisation limit 104591.01 cm⁻¹ = 12.96763 eV (95.611 nm)

Sources

• A. C. Stanton, Chem. Phys. Lett. 122, 385 (1985) (diode-laser absorption); experimental c…
• Alkhayat, Irving, Federman, Ellis, Cheng, Lifetimes and Oscillator Strengths for Ultravio…
• Alkhayat, Irving, Federman, Ellis, Cheng, Lifetimes and Oscillator Strengths for Ultravio…
• G. M. Lawrence, Astrophys. J. 148, 261 (1967), Table 7 (phase-shift method, stated accura…
• G. M. Lawrence, Astrophys. J. 148, 261 (1967), Table 7 (phase-shift method, stated accura…
• Holloway, Aubrey, King, Proc. Phys. Soc. 76, 984 (1960); King & Jaccarino, Phys. Rev. 84,…
• Kurucz, R. L., Can. J. Phys. 89, 417 (2011); semi-empirical line list gf1700.pos of 2013-…
• NIST ASD
• NIST ASD level energies
• Schectman, Federman, Beideck, Ellis, Astrophys. J. 406, 735 (1993) (beam-foil)
• Schectman, Federman, Beideck, Ellis, Astrophys. J. 406, 735 (1993) (beam-foil). Note: der…
• Schwab and Anderson (1982), absorption technique; Table 3 of Biemont, Gebarowski, Zeippen…
• atomic-beam magnetic resonance: Davis, Feld, Zabel, Zacharias, Phys. Rev. 76, 1076 (1949)…

Literature search was limited: the session's web-search quota was exhausted, so sources were located through Crossref, HAL, OSTI, arXiv and NASA ADS queries and only open copies could be read (APS, IOP, Elsevier, Canadian Science Publishing full texts were not accessible). Hyperfine constants of the ground term are second-hand from Chichinin's JPCRD review (method 'compilation'). Signs: A, B as printed (Casimir convention, E = A*C/2 + B*[...]). The M1 A value is the calculated one adopted by NIST. Values marked 'derived' were computed here from the quoted measured numbers. Two-photon entries: wavelength_vac_nm is the laser wavelength (two photons of that wavelength reach the upper level). Second pass (2026-10-01): beam-foil lifetimes of four more levels from arXiv:1910.05803; second-hand measured oscillator strengths of the 3p5 - 4s resonance lines read on the scanned Table 3 of Biemont et al. 1994 (NASA ADS; the image was checked by eye) and converted to A here (derived, method compilation). Lawrence-1967 entries in that table are listed only as alternatives because all but two of them come from an intermediate-coupling analysis of his lifetime measurements. Lines to 4s 4P levels are typed "intercombination".

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