LTE excitation and ionization populations
For a classical gas in local thermodynamic equilibrium, level ratios within one ionization stage obey N_b/N_a=(g_b/g_a)exp[−(E_b−E_a)/(k_BT)].
Key knowledge
For a classical gas in local thermodynamic equilibrium, level ratios within one ionization stage obey N_b/N_a=(g_b/g_a)exp[−(E_b−E_a)/(k_BT)]. Ionization balance additionally depends on electron density: n_{i+1}nₑ/n_i=2(U_{i+1}/U_i)(2πmₑk_BT/h²)³ᐟ²exp[−χ_i/(k_BT)]. Excitation and ionization both affect spectral-line inference.
Values and equations
N_b/N_a=(g_b/g_a)e^[−(E_b−E_a)/(k_BT)]; n_{i+1}nₑ/n_i=2(U_{i+1}/U_i)(2πmₑk_BT/h²)^(3/2)e^[−χ_i/(k_BT)]
- N_a,N_b
- populations of two levels within the same ionization stage counts
- g_a,g_b,U_i,U_{i+1}
- statistical weights and bounded internal partition functions 1
- E_a,E_b,χ_i
- level energies and stage ionization energy J
- n_i,n_{i+1},nₑ
- number densities of successive ionization stages and electrons m⁻³
- mₑ
- electron mass kg
- k_B
- Boltzmann constant J K⁻¹
- T
- local equilibrium temperature K
- h
- Planck constant J s
Conditions and scope
- U_i is the internal partition function with energies measured from that stage's ground state; χ_i is the energy from its ground state to the next ionization ground state. The explicit electron spin factor is2.
- Use nondegenerate particles and an appropriate finite partition model; an isolated atom's untruncated Rydberg sum diverges. Non-LTE irradiation, dense-plasma corrections and occupation probabilities require fuller models.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read the actual level ratio and partition/energy-zero/electron-spin definitions, including divergence of the untruncated atomic partition. Neglected ion/atom mass differences in the electron translational factor as stated; no blanket equation of matter LTE with a Planck radiation field or numerical photospheric ionization prediction.
2026-10-10 · Independent AI editorial review: All44 exact root-authored compact records, equations/variable units/conditions and140 origin edges accepted after independently reading final6/18 with bounded primary bodies and matching prior38/122 scientific fingerprints unchanged. Exact claim/edge review is distinct from combined inventory scope and separate CLE26 approval; no entire cited books or old-corpus experimental revalidation is asserted. Receipt: cosmos-completion-independent-content-and-inventory-review.1.
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