1. E /eV u^-1
2. sigma /cm²

• B7: R. K. Janev, J. J. Smith, "Cross sections for collision processes of hydrogen atoms with electrons, protons, and multiply charged ions", IAEA- Atomic and Plasma–Material Interaction Data for Fusion, Vienna 4 (1993). [https://www.iaea.org/publications/1839/atomic-and-plasma-material-interaction-data-for-fusion]

c
c###################################################################
c
      subroutine hexc1(pe, pcf, kncf, pxs, kermsg)
c
c     this is a subroutine to calculate cross sections (cm[2])
c     versus projectile energy (ev) for heavy particle collisions.
c
c     pe = collision energy in kev/amu
c
c     pcf(1-9) = parameters for fit to the cross section
c
c     kermsg = blank if no errors
c
c     pxs = cross section in 10e-16 cm[2]
c------------------------------------------------------------------------
c
      double precision pe, pcf, pxs
      double precision e, a1, a2, a3, a4, a5, a6, arg1, arg2, arg3
      double precision a7, a8, a9, c1, c2, c3, dexpr, zero, one
c
      dimension pcf(9)
      character*(*) kermsg
        data dexpr/7.00d+02/
        data zero/0.00d+00/
        data one/1.00d+00/
c
c     generate e, the energy in kev
c
      e = pe
c
      a1= pcf(1)
      a2= pcf(2)
      a3= pcf(3)
      a4= pcf(4)
      a5= pcf(5)
      a6= pcf(6)
      a7= pcf(7)
      a8= pcf(8)
      a9= pcf(9)
      arg1=-a2/e
      c1=zero
      if (dabs(arg1) .lt. dexpr) c1=dexp(arg1) /e
c
      arg2=-a4*e
      c2=zero
      if (dabs(arg2) .lt. dexpr) c2=a3*dexp(arg2)/(e**a5)
c
      arg3=-a7/e
      c3=zero
      if (dabs(arg3) .lt. dexpr) c3= a6*dexp(arg3)/
     1   (one + a8*(e**a9))
c
      pxs=a1*(c1 + c2 + c3)
      return
      end