      REAL FUNCTION SIGMA(E)
C     ELECTRON COLLISIONS WITH N2
C     SINGLE IONIZATION
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 /2.90E-2,2.50E+0,2.79E-2/
      DATA A /4.080E-5,1.700E+2,2.820E-1,1.026E+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