c
c###################################################################
c
      subroutine jeexc4(pe, pcf, kncf, pxs, kermsg)
c
c     this is a subroutine to calculate cross sections (cm[2])
c     versus energy (ev) for electron impact excitation for dipole
c     forbidden transitions with spin change.
c     the formula is taken from doc=h-he-plasma reaction 2.3.4
c
c     pcf is the coefficient data array, where
c
c     pcf(1) =   coefficient q for the transition
c
c     pcf(2) =   lin, the orbital angular monentum of the inital state
c
c     pcf(3) =   multi, spin multiplicity (2s+1) of the inital state
c
c     pcf(4) =   lfin, the orbital angular monentum of the final state
c
c     pcf(5) =   multf, spin multiplicity (2s+1) of the final 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 excitation energy for the transition (ev)
c
c     pe = electron energy (ev)
c
c     kermsg = blank if no errors
c
c     pxs = cross section in cm[2]
c
c------------------------------------------------------------------------
c
      double precision pe, pcf, pxs
c
      dimension pcf(6)
      integer lin, lfin, multi, multf
      character*(*) kermsg
c
      data ry /1.358e+01/
c
      q   = pcf(1)
      lin = pcf(2)
      multi = pcf(3)
      lfin = pcf(4)
      multf = pcf(5)
      kermsg = ' '
      if (kncf .eq. 5) then
c
c        first call to jeexc4 determine energy independent
c        parameters and place in pcf for further use
c
c        determine the threshold energy from the eneries of the initial
c        and final states
c
          call heexcen(2, lin, multi, 0, eexc1, kermsg)
          call heexcen(2, lfin, multf,0, eexc2, kermsg)
          eth = abs (eexc1 - eexc2)
c
c        place energy independent parameters in coefficient array and
c        update kncf
c
          pcf(6) = eth
          kncf = 6
      else if (kncf .eq. 6) then
          eth  = pcf(6)
c
      else
          kermsg = ' incorrect number of coefficients passed to jeexc4'
          return
      endif
c
      if (pe .lt. eth) then
        pxs  = 0.0
        return
      endif
c
      u = pe / eth
      pxs  = 3.52e-16 * q * (u - 1.0) / (u ** 2)
c
      return
c
      end