SUBROUTINE CARBON(IB,FR,SG)
C     ===========================
C
C     Photoionization cross-section for neutral carbon 2p1D and 2p1S
C     levels (G.B.Taylor - private communication)
C
      INCLUDE 'IMPLIC.FOR'
      DIMENSION FR2(34),SG2(34),FR3(45),SG3(45)
      PARAMETER (FR0=3.28805D15, NC2=34, NC3=45)
      DATA FR2/ 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82,
     *                0.83,       0.85, 0.86, 0.87, 0.88, 0.89, 0.90,
     *          0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99,
     *          1.00, 1.10, 1.20, 1.30, 1.45, 1.50, 1.60, 1.80, 2./
      DATA SG2/ 12.04, 12.03, 12.09, 12.26, 12.60, 13.24, 14.36, 16.24,
     *          19.28, 23.94, 37.41, 42.88, 44.76, 43.41, 40.46, 37.19,
     *          34.26, 31.82, 29.96, 28.57, 27.68, 27.37, 27.84, 29.69,
     *          34.45, 46.35, 13.80, 11.54, 10.40,  8.96,  8.54,  7.47,
     *           6.53,  5.66/
      DATA FR3/ 0.66, 0.68, 0.70, 0.72, 0.74, 0.76, 0.78, 0.80, 0.82,
     *          0.84, 0.86, 0.864,0.866,0.868,0.87, 0.874,0.876,0.88,
     *          0.882,0.884,0.886,0.888,0.89 ,0.894,0.896,0.898,0.90,
     *          0.904,0.908,0.910,0.920,0.94, 0.98, 1.00, 1.10, 1.20,
     *          1.26, 1.34, 1.36, 1.40, 1.46, 1.60, 1.70, 1.80, 2./
      DATA SG3/ 13.94, 13.29, 12.56, 11.73, 10.82, 10.18,  8.62,  7.27,
     *           5.74,  4.14,  4.61,  5.92,  6.94,  8.34, 10.21, 16.12,
     *          20.64, 34.56, 44.82, 57.71, 73.09, 89.99,106.38,127.08,
     *         128.38,124.44,117.17, 99.32, 82.95, 76.05, 52.65, 33.23,
     *          21.29, 18.69, 12.62, 11.44,  9.77,  7.53, 10.47,  9.65,
     *          10.19,  7.28,  6.70,  6.11,  4.96/
      SAVE FR2,SG2,FR3,SG3
C
      F=FR/FR0
      IF(IB.NE.-602) GO TO 25
      J=2
      IF(F.LE.FR2(1)) GO TO 20
      DO I=2,NC2
         J=I
         IF(F.GT.FR2(I-1).AND.F.LE.FR2(I)) GO TO 20
      END DO
   20 SG=(F-FR2(J-1))/(FR2(J)-FR2(J-1))*(SG2(J)-SG2(J-1))+SG2(J-1)
      SG=SG*1.D-18
   25 IF(IB.NE.-603) GO TO 50
      J=2
      IF(F.LE.FR3(1)) GO TO 40
      DO I=2,NC3
         J=I
         IF(F.GT.FR3(I-1).AND.F.LE.FR3(I)) GO TO 40
      END DO
   40 SG=(F-FR3(J-1))/(FR3(J)-FR3(J-1))*(SG3(J)-SG3(J-1))+SG3(J-1)
      SG=SG*1.D-18
   50 CONTINUE
      RETURN
      END