/* ------------- file: -------------------- saha.c ------------------- */

/* Evaluates: the Boltzmann equilibrium relation
 *   input  - statisical weights of different energy levels
 *          - temperature
 *          - energy difference levels in J
 *   output - ratio nj/ni, dimensionless

 * Evaluates the Saha equilibrium relation
 *   input  - statisical weights of different ionization stages
 *          - temperature
 *          - ionization energy in J
 *          - electron density (or set to 1)
 *   output - ratio ni/(nc*ne) in units of m^3.
 *       OR - ratio ni/nc unitless if ne is input as 1
 *
 * Sara Seager
 * Last modified: July 11, 1995
 */

#include <math.h>
#include "constant.h"

/* -----------begin -----------------------Boltzmann.c---------------------- */

double Boltzmann(double gj, double gi, double E, double T )
{
/* --- Computes nj/ni  where j is the higher level             ------------- */

  return ( (gj/gi) * exp(-E/(kBoltz*T)) );
}
/* ----------end -------------------------Boltzmann.c ---------------------- */

/* --------- begin ----------------------- SahaBoltz.c --------------------- */

double SahaBoltz(double gi, double gc, double ne, double E_ion, double T)
{
/* --- the form is ni/(nc*ne) i is the lower ionization state -------------- */

  double c1;
  c1 = (hPlanck/(2.0*PI*mElect)) * (hPlanck/kBoltz);
  return (ne * gi/(2.0*gc) * pow(c1, 1.5) * pow(T, -1.5) * 
	  exp(E_ion/(kBoltz*T)) );
}

/* ----------- end -------------------- SahaBoltz.c ------------------------ */