      REAL FUNCTION SIGMA(E)
C     ELECTRON COLLISIONS WITH CO2
C     TOTAL SCATTERING
C     CROSS SECTION(CM^2)  :SIGMA
C     COLLISION ENERGY(KEV):E
C     T.Shirai, et al., At. Data Nucl. Data Tables 79, 143 (2001).
      REAL A(12)
      DATA EMIN,EMAX,ETH /5.00E-4,5.00,0.00/
      DATA A /5.820E-1,-9.950E-1,8.870E+4,6.760,3.882E-3,1.030E+1,
     >        2.990E+1,1.490,1.310E-2,2.200E-1,3.300E-2,9.300E-1/
      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=F1(SIGMA0,ER,E1,A(1),A(2))
     >     +F2(SIGMA0,ER,E1,A(3),A(4),A(5),A(6))
     >     +F3(SIGMA0,ER,E1,A(7),A(8),A(9),A(10),A(11),A(12))
 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

