1. E /eV
2. sigma /cm²

• B57: R. K. Janev, J. J. Smith, F. Aumayr, D. Wutte, M. Schneider, H. P. Winter, J. Schweizer, "Atomic collision database for Li beam interaction with fusion plasmas", IAEA, Vienna 267 (1993). [https://www-nds.iaea.org/publications/indc/indc-nds-0267/]

def eionlt(pe, pcf, kncf):
    """
    This function calulates electon-impact ionization cross sections(cm2)
    as a function of energy in eV.

    pe:collision energy in eV
    pcf: parameter data array
        pcf[0]: binding energy of the electron in first subshell
        pcf[1]: binding energy of the electron in second subshell
        pcf[2:10]: parameters for analytic function
    """
    eth1 = pcf[0]
    if pe >= eth1:
        if kncf == 10:
            eth2 = pcf[1]
            xs1 = pcf[4] * pcf[2] * np.log(pe/eth1) * 
                          (1.0 - pcf[6] * np.exp(-pcf[8] * (pe / eth1 - 1.0))) / eth1
            xs2 = pcf[5] * pcf[3] * np.log(pe/eth2) * 
                          (1.0 - pcf[7] * np.exp(-pcf[9] * (pe / eth2 - 1.0))) / eth2
            pxs = 1.0e-14 * (xs1 + xs2) / pe
            return pxs
        else:
            raise ValueError('Incorrect number of coefficients passed to eionlt')
    else:
        raise ValueError('Energy below threshold for ionization')

c
c###################################################################
c
      subroutine eionlt(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
c     pe = collision energy in eV
c
c     this evaluation function requires the binding energies of the
c     target atomic subshells and constants to be passed in the coefficient 
c     data array, such that
c
c     pcf(1) = binding energy of the electron in first subshell
c     pcf(2) = binding energy of the electron in second subshell
c     pcf(3-4) = q1, q2
c     pcf(5-6) = a1, a2
c     pcf(7-8) = b1, b2
c     pcf(9-10) = c1, c2
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.
c
c     kermsg = blank if no errors
c
c     pxs = cross section in cm[2]
c
c------------------------------------------------------------------------
c
      double precision e, pe, pcf, pxs
      double precision eth1, eth2, xs1, xs2
      double precision a1, a2, b1, b2, c1, c2, q1, q2
c
      dimension pcf(10)
      character*(*) kermsg
c
      eth1 = pcf(1)
      if(pe .ge. eth1) then
        kermsg = ' '
      else
        pxs = 0.0
        return
      endif
c
c energy remains in eV
      e = pe
c
c     determine the value of the cross section  pxs
c
      if(kncf .eq. 10) then
        eth2 = pcf(2)
        q1 = pcf(3)
        q2 = pcf(4)
        a1 = pcf(5)
        a2 = pcf(6)
        b1 = pcf(7)
        b2 = pcf(8)
        c1 = pcf(9)
        c2 = pcf(10)
        xs1 = a1 * q1 * dlog(e/eth1) * 
     1    (1.d0-b1*dexp(-c1*(e/eth1 - 1.d0)))/eth1
        xs2 = a2 * q2 * dlog(e/eth2) * 
     1    (1.d0-b2*dexp(-c2*(e/eth2 - 1.d0)))/eth2
        pxs = 1.0e-14 * (xs1 + xs2)/e
      else
          kermsg = ' incorrect number of coefficients passed to eionlt'
          return
      endif
c
      return
      end