**Saha**__
Equation__

The

Saha equationcan be expressed as

N_{q+1}N/_{e}N_{q }= [(2πm)_{e}kT^{3/2}/h^{3}][2u_{q+1}(T)/u(_{q}T)]exp(-I,/_{q}kT)where

N_{q+1}total_{ }=number of particles per unit volume in theq+1^{th}ionization state of the element under consideration, (N_{q+1}= Σ_{ r}N),_{q+1,r}

N_{q}total_{ }=number of particles per unit volume in theq^{th}ionization state of the element under consideration, (N_{q}= Σ_{ r}N),_{q,r}

N_{e}total_{ }=number of free electrons per unit volume,

= Σu(_{q+1}T)_{ r}gexp(-_{q+1,r}χ/_{q+1,r}kT) is thepartition functionfor theq+1^{th}ionization state, ther^{th}term of which is proportional to the number

of particles (per unit volume) in ther^{th}level of excitation,

= Σu(_{q}T)_{ r}gexp(-_{q,r}χ/_{q,r}kT) is thepartition functionfor theq^{th}ionization state, ther^{th}term of which is proportional to the number of

particles (per unit volume) in ther^{th}level of excitation,

= the stistical weight of theg_{q,r}r^{th}excited level of theq^{th}ionization state,

= the excitation energy of theχ_{q,r}r^{th}excited level with respect to the ground level of theq^{th}ionization state,

= the ionization energy of theI_{q}q+1^{th }ionization state with respect to the ground state of theq^{th }ionization state,

= the electron mass = 9.1093897 ´ 10m_{e}^{-28}g,

= Planck's constant = 6.6260755 ´ 10h^{-27}erg s,

= Boltzmann's constant = 1.380622 ´ 10k^{-16}erg/K = 8.61779 ´ 10^{-5}eV/K, and

= the temperature expressed in Kelvins.TNote that the Saha equation can also be written

N_{q+1}P/_{e}N_{q }= [(2πm)_{e}^{3/2}/h^{3}](kT)^{5/2}[2u_{q+1}(T)/u(_{q}T)]exp(-I,/_{q}kT)where

is the electron pressure in dyn cmP_{e }= N_{e}kT^{-2}.The logarithmic form of the Saha Equation is

log (N_{q+1}/N_{q}) = -θI[eV] + 2.5 log_{q }T- 0.48 + log[2u_{q+1}(T)/u(_{q}T)] - logP_{e},where

θº 5040/T.