      REAL FUNCTION SIGMA(E)
C     ELECTRON COLLISIONS WITH C2H4
C     MOMENTUM TRANSFER
C     CROSS SECTION(CM^2)  :SIGMA
C     COLLISION ENERGY(KEV):E
C     T.Shirai, et al., At. Data Nucl. Data Tables 80, 147 (2002).
      REAL A(13)
      DATA EMIN,EMAX,ETH /1.03E-5,1.00,0.0/
      DATA A /1.420E-1,-5.920E-1,6.140E-5,9.400,4.090E+11,5.180,
     >        1.103E-4,-5.510E-1,2.750E-4,1.494,1.890E+1,6.730E-1,
     >        2.050E-2/
      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=F2(SIGMA0,ER,E1,A(1),A(2),A(3),A(4))
     >     +F3(SIGMA0,ER,E1,A(5),A(6),A(7),A(8),A(9),A(10))
     >     +F2(SIGMA0,ER,E1,A(11),A(12),A(13),A(10))
 9999 RETURN
      END
C
      REAL FUNCTION F1(SIGMA0,ER,X,C1,C2)
        F1=SIGMA0*C1*(X/ER)**C2
      RETURN
      END
C
      REAL FUNCTION F2(SIGMA0,ER,X,C1,C2,C3,C4)
        F2=SIGMA0*C1*(X/ER)**C2
     >     /(1.+(X/C3)**(C2+C4))
      RETURN
      END
C
      REAL FUNCTION F3(SIGMA0,ER,X,C1,C2,C3,C4,C5,C6)
        F3=SIGMA0*C1*(X/ER)**C2
     >     /(1.+(X/C3)**(C2+C4)+(X/C5)**(C2+C6))
      RETURN
      END

