ADAS Subroutine r8fbch

      FUNCTION R8FBCH( IZ , XI , ZETA , TE )
C-----------------------------------------------------------------------
C
C  **************** FORTRAN77 REAL*8 FUNCTION: R8FBCH ******************
C
C  PURPOSE: EVALUATES A SHELL CONTRIBUTION TO THE IONISATION RATE COEFF-
C           ICIENT IN THE BURGESS-CHIDICHIMO APPROXIMATION.
C
C  REFERENCE: MNRAS.(1983)203,1269.
C
C  CALLING PROGRAM: GENERAL USE
C
C  FUNCTION:
C          (R*8)  R8FBCH  = FUNCTION NAME
C          (I*4)  IZ      = TARGET ION CHARGE NUMBER
C                           (RECOMBINED ION CHARGE).
C          (R*8)  XI      = EFFECTIVE IONISATION POTENTIAL FOR SHELL
C                           (UNITS: RYDBERGS)
C                           (LEVEL ENERGY RELATIVE TO IONISATION POT.)
C          (R*8)  ZETA    = EFFECTIVE NUMBER OF EQUIVALENT ELECTRONS
C                           IN SHELL
C          (R*8)  TE      = ELECTRON TEMPERATURE (IN KELVIN)
C
C          (R*8)  C       = PARAMETER = EQUATION CONSTANT = 2.3
C          (R*8)  DXIPOW  = PARAMETER = EQUATION CONSTANT = 1.5
C          (R*8)  TK2ATE  = PARAMETER = EQUATION CONSTANT = 1.5789D+05
C          (R*8)  R2GAM   = PARAMETER = EQUATION CONSTANT = 2.17161D-08
C          (R*8)  D150    = PARAMETER = 150
C          (R*8)  CR2GAM  = PARAMETER = EQUATION CONSTANT = 'C'*'R2GAM'
C
C          (R*8)  BETA    = EQUATION CONSTANT (SEE NOTE BELOW)
C          (R*8)  Y       =
C          (R*8)  T1      =
C          (R*8)  W       =
C          (R*8)  P       = TEMPORARY PARAMETER STORAGE
C
C ROUTINES:
C          ROUTINE    SOURCE    BRIEF DESCRIPTION
C          -------------------------------------------------------------
C          R8FEEI     ADAS      FUNCTION:
C
C NOTE:
C                         (100*IZ) + 91
C                   SQRT( ------------- ) - 5
C                          (4*IZ) + 3
C           BETA =  -------------------------
C                               4
C
C
C AUTHOR:   PAUL E. BRIDEN (TESSELLA SUPPORT SERVICES PLC)
C           K1/0/81
C           JET EXT. 4569
C
C DATE:     04/09/90
C
C VERSION  : 1.2                          
C DATE     : 20-12-2001
C MODIFIED : Martin O'Mullane
C               - Removed mainframe listing information beyond column 72.
C
C-----------------------------------------------------------------------
C-----------------------------------------------------------------------
      INTEGER             IZ
      REAL*8              TE,          XI,          ZETA