subroutine dsg0(val,eval)

      implicit none

      integer i,n
      parameter(n=13)
      double precision temp(n), dsig0(n)
      double precision val,eval,slop,y_int

c  From Tsipenyuk, Fig. 3  dSIG/dOmega(q=0)

      data temp/1.600000, 1.800000, 2.000000, 2.200000, 2.400000,
     &     2.600000, 2.800000, 3.000000, 3.200000, 3.400000, 3.600000,
     &     3.800000, 4.000000/  ! K
      data dsig0/0.1433225d-03, 0.1622665d-03, 0.1820104d-03,
     &     0.2010544d-03, 0.2240130d-03, 0.2470570d-03, 0.2730156d-03,
     &     0.2990743d-03, 0.3382476d-03, 0.3928795d-03, 0.4820847d-03,
     &     0.6123778d-03, 0.7687297d-03/ ! cm^-1

      do i=1,n-1
         if(val.lt.temp(1)) then
            eval = dsig0(1)
         elseif(val.eq.temp(i)) then
            eval = dsig0(i)
         elseif(val.eq.temp(i+1)) then
            eval = dsig0(i+1)
         elseif(val.gt.temp(i).and.val.lt.temp(i+1)) then
            slop = (dsig0(i+1)-dsig0(i))/(temp(i+1)-temp(i))
            y_int = dsig0(i) - slop*temp(i)
            eval = slop*val+y_int
         elseif(val.gt.temp(i+1)) then
            slop = (dsig0(i+1)-dsig0(i))/(temp(i+1)-temp(i)) ! bec "i-1 to i"
            y_int = dsig0(i) - slop*temp(i)				   ! bec "i-1 to i"
            eval = slop*val+y_int
         endif
      enddo

      return
      end