FUNCTION CEH12(T)
C     =================
C
C     Special formula for collisional rate in hydrogen Lyman-alpha
C     transition
C     After Crandall et al. Ap.J. 191, 789 (1974)
C
      INCLUDE 'IMPLIC.FOR'
      DIMENSION A(6),B(8)
      PARAMETER (C=-118353.41)
      DATA A/ 2.579997D-10, -1.629166D-10,  7.713069D-11,
     *       -2.668768D-11,  6.642513D-12, -9.422885D-13/
      SAVE A
c
      DO  I=1,8
         B(I)=0.
      END DO
      X=LOG10(T)-4.
      DO I=1,6
         J=7-I
         B(J)=2.*X*B(J+1)-B(J+2)+A(J)
      END DO
      CEH12=2.4*SQRT(T)*(B(1)-B(3))*EXP(C/T)
      RETURN
      END