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/* This file is part of Cloudy and is copyright (C)1978-2008 by Gary J. Ferland and
 * others.  For conditions of distribution and use see copyright notice in license.txt */
/*ligbar obtain collision strength for any Li-sequence line */
#include "cddefines.h"
#include "physconst.h"
#include "dense.h"
#include "phycon.h"
#include "ligbar.h"

void ligbar(long int ized, 
  transition * t2s2p, 
  transition * t2s3p, 
  double *cs2s2p, 
  double *cs2s3p)
{
        double a, 
          b, 
          c, 
          excit, 
          gbar;

        DEBUG_ENTRY( "ligbar()" );

        /* compute collision strength for Li-seq g-bar approx
         * summarized in Cochrane and McWhirter Physica Scripta 28, 25.
         * ized is nuclear charge, can be anything larger than 2
         * Kirk Korista
         *
         * ized is nuclear charge, 6 for carbon, etc
         * t2s2p is tau array for stronger memeber of 2s 2p multiplet,
         * which is treated as two separate lines
         * t2s3p is next transition up, treated as an averaged multiplet
         *
         * cs2s2p is the cs for the single 2s2p line that comes in
         * cs2s3p is the multiplet cs for that transition, which is
         * treated as  a multiplet average.  If t2s3p is ever separated
         * (as t2s2p was) then cs2s3p will be the single line not the multiplet
         *
         * T2S2P, T2S3P are line information array, defined in block data
         */

        /* no need to evaluate coll strength if population is zero */
        if(dense.xIonDense[ t2s2p->Hi->nelem -1 ][ t2s2p->Hi->IonStg-1 ] == 0)
        {
                *cs2s2p = 1.;
                *cs2s3p = 1.;
                return;
        }

        if( ized < 3 )
        {
                /* this is a sanity check */
                fprintf( ioQQQ, " LIGBAR called with insane charge, ized=%4ld\n", 
                  ized );
                ShowMe();
                cdEXIT(EXIT_FAILURE);
        }

        else if( ized == 6 )
        {
                /* CIV 1549 */
                a = 0.292;
                b = 0.289;
                c = 2.67;
        }

        else if( ized == 7 )
        {
                /* NV 1240 */
                a = 0.387;
                b = 0.247;
                c = 3.93;
        }

        else if( ized == 8 )
        {
                /* OVI 1035 -- values interpolated */
                a = 0.40;
                b = 0.256;
                c = 4.12;
        }

        else if( ized == 10 )
        {
                /* NeVIII 774 */
                a = 0.426;
                b = 0.273;
                c = 4.50;
        }

        else if( ized == 12 )
        {
                /* Mg 10 615 -- these values are general */
                a = 0.45;
                b = 0.27;
                c = 5.0;
        }

        else if( ized == 18 )
        {
                /* Ar 16 365 */
                a = 0.311;
                b = 0.294;
                c = 6.65;
        }

        else if( ized == 26 )
        {
                /* Fe 24 213 */
                a = 0.435;
                b = 0.314;
                c = 6.92;
        }

        else
        {
                /* use general formula for all other cases */
                a = 0.6 - 1.5/((realnum)(ized) - 2.);
                b = 0.27;
                c = 5.;
        }

        /* evaluate expression in terms of coefficients
         * tarray(ipLnBolt) = line energy in degrees kelvin */
        excit = t2s2p->EnergyK/phycon.te;

        /* excit = e1/(te * 1.380622e-16) */
        gbar = a + b*log(1./excit+c);

        /* tarray(ipLnGF) = gf; tarray(ipLnBolt) excit temp kelvin */
        /*
        *cs2s2p = gbar*197.47*EVDEGK*t2s2p->Lo->gf/t2s2p->EnergyK;
        */
         *cs2s2p = gbar*197.47*EVDEGK*t2s2p->Emis->gf/t2s2p->EnergyK;
        /* small correction factors to CMcW83 2s-2p fits:
         * fits 3.57% too small compared to R-matrix calc. for Mg X.
         * scaled all, initially, by this constant. Pradhan & Peng (1994)
         * compilation cites a pc with Burgess, which further scales
         * cs(C IV) by 1.0429 and cs(N V) by 0.9691, approximately. 
         * The scaled cs(OVI) matched well with Burgess, so no further
         * scaling was done for more highly ionized species. */

        if( ized == 6 )
        {
                *cs2s2p *= 1.08013;
        }

        else if( ized == 7 )
        {
                *cs2s2p *= 1.00370;
        }

        else
        {
                *cs2s2p *= 1.0357;
        }


        /* use general formula for 2s3p */
        a = -0.244;
        b = 0.25;
        c = 4.;

        /* excit = e2/(te * 1.380622e-16) */
        excit = t2s3p->EnergyK/phycon.te;
        gbar = a + b*log(1./excit+c);
        /* tarray(ipLnGF) = gf */
     *cs2s3p = gbar*197.47*EVDEGK*t2s3p->Emis->gf/t2s3p->EnergyK;
        /* cs2s3p = gbar * 197.47*eVdegK *  GF2/(e2/1.60184e-12)
         * */
        return;
}

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