C
      function anu(xxnu,ipt)
C
C xxnu: frecuencia
C ipt:  H=1, He0=2, He+=3
C
C Calculo de las secciones eficaces del H, He0, He+
C segun los ajustes de Verner et al, 1996, ApJ, 465, 487
C tomados de: http://www.pa.uky.edu/~verner/photo.html
C
C Enrique. INAOE. Abril 2001.
C
      e0=6.62d-27*xxnu/1.602192d-12
      if (ipt.eq.1) then
C
C H
C
         en=e0/0.4298
         anu=54750.*(en-1.)**2./(en**4.0185*(1.+sqrt(en/32.88))**2.963)
         anu=anu*1.d-18
         return
      else if (ipt.eq.2) then
C
C He0
C
         en=e0/13.61-0.4434
         anu=949.2*((en-1.)**2.+4.157521)/
     -      (en**2.+4.562496)**1.953 / 
     -      ((1.+0.82506685*(en**2.+4.562496)**0.25)**3.188)
         anu=anu*1.d-18
         return
      else if (ipt.eq.3) then
C
C He+
C
         en=e0/1.72
         anu=13690.*(en-1.)**2. /
     -      en**4.0185 / 
     -      (1.+0.174395*en**0.5)**2.963
         anu=anu*1.d-18
         return
      else
         write(*,'('' ***** ERROR in cross sections *****'')')
      endif
      return
      end