      REAL FUNCTION SIGMA(E)
C     ELECTRON COLLISIONS WITH N2
C     N^+ + N PRODUCTION
C     CROSS SECTION(CM^2)  :SIGMA
C     COLLISION ENERGY(KEV):E
C     T.Tabata, et al., At. Data Nucl. Data Tables.
      REAL A(12)
      DATA EMIN,EMAX,ETH /2.50E-2,6.00E-1,1.80E-2/
      DATA A /5.060E-4,2.640E-1,3.540E-2,2.362E+0,8*0.0/
      DATA SIGMA0,ER /1.E-16,1.361E-2/
      SIGMA=0.0
      IF(E.LT.EMIN .OR. E.GT.EMAX) GO TO 9999
      E1=E-ETH
      SIGMA=SIGMA0*A(1)*(ALOG(E/ETH)+A(2))/
     >      (ETH*E*(1.+(A(3)/E1)**A(4)))
 9999 RETURN
      END