c###################################################################
c
      subroutine heionen(n, l, mult, sumen, eion, kermsg)
c
c     this subroutine passes the ionization energy for excited states
c     of  helium taken from tables a.4 and a.5 given by janev et al.
c     (see doc=h-he-plasma.)
c
c     the input subroutine parameters are
c
c    n = principal quantum number of the excited electronic state
c
c    l = orbital angular momentum quantum number of the exited state
c
c    mult = the spin multiplicity (2s+1) of the state
c
c    sumen =  indicates choice of ionization energy to be returned.
c             if sumen=0  the ionization energy for the specific
c              state (quantified by n, l amd mult) is returned
c             if sumen=1  the ionization energy taken as an average
c             over angular momentum and toatal spin is returned
c
c     the output subroutine parameters are
c
c    eion = ionization energy
c
c    kermsg = blank if no errors
c
c     written by j. j. smith , iaea atomic and molecular data unit
c
c------------------------------------------------------------------------
c
      character*(*) kermsg
      integer n, l, mult, sumen, lp, multp
      dimension enl(4,4,2), en(7)
      data (((enl(i,j,k),i=1,4),j=1,4),k=1,2) /32*0.0/
c
c     data enl(1,1,1)
c    *    / 24.588 /,
c
c----   n=2 excited states
c
c    1  enl(2,1,1),enl(2,1,2),enl(2,2,1),enl(2,2,2)
c    *    / 3.973, 4.769, 3.371, 3.625 /,
c
c----   n=3 excited states
c
c    2   enl(3,1,1),enl(3,1,2),enl(3,2,1),enl(3,2,2),enl(3,3,1),
c    *   enl(3,3,2)
c    *    / 1.699, 1.871, 1.502, 1.582, 1.515, 1.515 /,
c
c----   n=4 excited states
c
c    3   enl(4,1,1),enl(4,1,2),enl(4,2,1),enl(4,2,2),enl(4,3,1),
c    *   enl(4,3,2),enl(4,4,1),enl(4,4,2)
c    *    / 0.9155, 0.9951, 0.8470, 0.8812, 0.8529, 0.8530, 0.8520,
c    *      0.8520 /
c
c-----   ionization energies summed over angular momentum and
c-----   total spin
c
      data (en(k),k=1,2) /2*0.0/
      data en(3),en(4),en(5),en(6),en(7)
     *    / 1.609 , 0.8811, 0.52, 0.37, 0.29/
c
      enl(1,1,1)=24.588
c----   n=2 excited states
      enl(2,1,1)=3.973
      enl(2,1,2)=4.769
      enl(2,2,1)=3.371
      enl(2,2,2)=3.625
c----   n=3 excited states
      enl(3,1,1)=1.699
      enl(3,1,2)=1.871
      enl(3,2,1)=1.502
      enl(3,2,2)=1.582
      enl(3,3,1)=1.515
      enl(3,3,2)=1.515
c----   n=4 excited states
      enl(4,1,1)=0.9155
      enl(4,1,2)=0.9951
      enl(4,2,1)=0.8470
      enl(4,2,2)=0.8812
      enl(4,3,1)=0.8529
      enl(4,3,2)=0.8530
      enl(4,4,1)=0.8520
      enl(4,4,2)=0.8520
      kermsg =' '
      if (sumen .eq. 1) then
        if (n .ge. 8) then
          eion =13.58/(n*n)
          return
        else
           eion =en(n)
           if (eion .eq. 0.0) kermsg =
     *        'ionization energy for n value not in table in heionen'
        endif
      else
           lp = l+1
           if (mult .eq. 1) then
             multp = 1
           else if (mult .eq. 3) then
               multp = 2
             else
                 kermsg = 'invalid spin multipclity as input in heionen'
             endif
           eion = enl(n,lp,multp)
           if (eion .eq. 0.0) kermsg =
     *        'ionization energy not in table in heionen'
      endif
      return
      end
c###################################################################

c###################################################################
c
      subroutine jionhe(pe, pcf, kncf, pxs, kermsg)
c
c     this is a subroutine to calculate cross sections (cm[2])
c     versus energy (ev) for electron impact ionization.
c     for details see doc=h-he-plasma , used for  reactions
c     2.3.10, 2.3.11 (see doc=h-he-plasma.)
c
c     pe = collision energy in ev
c
c     the coefficient data array passed should contain
c
c     pcf(1)  =  itrans,  integer which defines the type of transition.
c                 for transitions defined only in terms of the initial
c                 and final principal quantum numbers (n,m), itrans=1.
c                 for tranitions between (nl,ml') states itrans=2
c
c     pcf(2)  =  value of coefficient beta
c
c     pcf(3)  =  n, principal quantum number of initial state
c
c     if itrans = 2 the following coefficients are required
c
c     pcf(4) =   l, the orbital angular monentum of the inital state
c
c     pcf(5) =   mult, spin multiplicity (2s+1) of the inital state
c
c    - warning- .
c
c        the coefficient array pcf is updated by this routine to
c     include energy independent constants. these coefficients can be
c     used in subsequent calls for the same entry. the coefficeients
c     added are:
c
c     pcf(6) = eth, threshold ionization energy for the transition (ev)
c
c     kermsg = blank if no errors
c
c     pxs = cross section in cm[2]
c
c     update d. humbert, 12 March 2007 ---- parameters passed to heionen changed
c------------------------------------------------------------------------
c
      double precision pe, pcf, pxs
c
      integer  n, l, m, itrans
      dimension pcf(6)
      character*(*) kermsg
c
      data ry /1.358e+01/
c
      itrans = pcf(1)
      beta   = pcf(2)
      n  = pcf(3)
      if (itrans .eq. 2) then
        l   = pcf(4)
        m   = pcf(5)
      endif
c
      if (kncf .lt. 6) then
c
c        first call to jionhe determine energy independent
c        parameters and place in pcf for further use
c
c        determine ionization energy
c
        if (itrans .eq. 1) then
          call heionen(n, 0, 0, 1, eion, kermsg)
        else if (itrans .eq. 2) then
          call heionen(n, l, m, 0, eion, kermsg)
        else
            kermsg = 'invalid value of fisrt coefficientin jionhe'
            return
        endif
c
c        place energy independent parameters in coefficient array and
c        update kncf
c
        pcf(6) = eion
        kncf = 6
      else if (kncf .eq. 6) then
          eion =  pcf(6)
c
      else
          kermsg = ' incorrect number of coefficients passed to jionhe'
          return
      endif
c
      if(pe .lt. eion) then
        pxs=0.0
        return
      endif
c
c     determine the value of the cross section  pxs
c
      u = pe/eion
      pxs = 3.52e-16 * (ry/eion)**2 * 0.66 * (u - 1.0) *
     1               log(1.25 * beta * u) / (u * u)
c
      return
      end

def heionen(n, l, mult, sumen):
    """
    This function passes the ionization energy for excited states of helium 
    taken from tables a.4 and a.5 given by janev et al.
 
    n: principal quantum number of the excited electronic state
    l: orbital angular momentum quantum number of the exited state
    mult: the spin multiplicity (2s+1) of the state
    sumen: indicates choice of ionization energy to be returned.
    """
    enl = np.zeros((4, 4, 2))
    en = np.zeros(7)
    
    # Define the ionization energy values
    enl[0, 0, 0] = 24.588
    enl[1, 0, 0] = 3.973
    enl[1, 0, 1] = 4.769
    enl[1, 1, 0] = 3.371
    enl[1, 1, 1] = 3.625
    enl[2, 0, 0] = 1.699
    enl[2, 0, 1] = 1.871
    enl[2, 1, 0] = 1.502
    enl[2, 1, 1] = 1.582
    enl[2, 2, 0] = 1.515
    enl[2, 2, 1] = 1.515
    enl[3, 0, 0] = 0.9155
    enl[3, 0, 1] = 0.9951
    enl[3, 1, 0] = 0.8470
    enl[3, 1, 1] = 0.8812
    enl[3, 2, 0] = 0.8529
    enl[3, 2, 1] = 0.8530
    enl[3, 3, 0] = 0.8520
    enl[3, 3, 1] = 0.8520
    en[2:5] = [1.609, 0.8811, 0.52, 0.37, 0.29]
    
    eion = 0.0
    
    if sumen == 1:
        if n >= 8:
            eion = 13.58 / (n * n)
        else:
            try:
                eion = en[n - 1]
            except IndexError:
                raise ValueError('Ionization energy for n value not in table in heionen')
    else:
        lp = l + 1
        if mult == 1:
            multp = 1
        elif mult == 3:
            multp = 2
        else:
            raise ValueError('Invalid spin multiplicity as input in heionen')
        
        try:
            eion = enl[n - 1, lp - 1, multp - 1]
        except IndexError:
            raise ValueError('Ionization energy not in table in heionen')
    
    return eion

##############################################################

def jionhe(pe, pcf, kncf):
    """
    This is a function to calculate cross sections (cm^2) versus energy (eV)
    for electron impact ionization.
    
    pe: collision energy (eV)
    pcf: coefficient data array
    kncf: number of coefficients
    """
    
    ry = 13.58
    
    itrans = int(pcf[0])
    beta = pcf[1]
    n = int(pcf[2])
    
    l = None
    m = None
    if itrans == 2:
        l = int(pcf[3])
        m = int(pcf[4])

    # Initialize energy-independent parameter
    eion = 0.0

    if kncf < 6:
        # First call to jionhe determines energy-independent parameters
        # and places them in pcf for further use

        try:
            if itrans == 1:
                eion = heionen(n, 0, 0, 1)
            elif itrans == 2:
                eion = heionen(n, l, m, 0)
            else:
                raise ValueError("Invalid value of first coefficient in jionhe")
        except ValueError:
            raise ValueError("Error calculating ionization energy")

        # Place energy-independent parameters in the coefficient array and update kncf
        pcf[6] = eion
        kncf = 6

    elif kncf == 6:
        eion = pcf[6]
    else:
        raise ValueError("Incorrect number of coefficients passed to jionhe")

    if pe < eion:
        pxs = 0.0
    else:
        u = pe / eion
        pxs = 3.52e-16 * (ry / eion) ** 2 * 0.66 * (u - 1.0) * np.log(1.25 * beta * u) / (u * u)

    return pxs