hydrooscilstr.cpp

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/* This file is part of Cloudy and is copyright (C)1978-2022 by Gary J. Ferland and
 * others.  For conditions of distribution and use see copyright notice in license.txt */
/*HydroOscilStr computes hydrogenic oscillator strengths, used in the function hdexct. */
#include "cddefines.h"
#include "hydrooscilstr.h"
#include "physconst.h"

double HydroOscilStr(double xLower, 
  double Upper)
{
        double fosc_v, 
          gaunt, 
          gnt0, 
          gnt1, 
          gnt2, 
          x;

        DEBUG_ENTRY( "HydroOscilStr()" );

        /*      >>refer H1      As      Johnson L.C., 1972 ApJ 174 227*/
        /* check order, and that none negative */
        ASSERT( xLower < Upper );
        ASSERT( xLower*Upper >0 );

        x = 1.0 - POW2(xLower/Upper);
        if( xLower >= 3 )
        {
                gnt0 = 0.9935 + 0.2328/xLower - 0.1296/xLower/xLower;
                gnt1 = -(0.6282 - 0.5598/xLower + 0.5299/xLower/xLower)/xLower;
                gnt2 = (0.3887 - 1.181/xLower + 1.470/xLower/xLower)/xLower/
                  xLower;
        }
        else if( xLower == 2 )
        {
                gnt0 = 1.0785;
                gnt1 = -.2319;
                gnt2 = 0.02947;
        }
        else
        {
                gnt0 = 1.1330;
                gnt1 = -.4059;
                gnt2 = 0.07014;
        }
        gaunt = gnt0 + gnt1/x + gnt2/x/x;
        fosc_v = 32./3./PI/sqrt(3.)*xLower/POW3(Upper)*gaunt/x/x/x;
        return( fosc_v );
}