SUBROUTINE DWNFR1(FR,FR0,ID,IZZ,DW1)
C     ====================================
C
C     dissolved fraction for frequency FR
C
      INCLUDE 'PARAMS.FOR'
      INCLUDE 'MODELP.FOR'
      PARAMETER (UN=1.,TKN=3.01,CKN=5.33333333,CB=8.59d14)
      PARAMETER (SQFRH=5.734152D7)
      parameter (a0=0.529177e-8,wa0=-3.1415926538/6.*a0*a0*a0)
C
      IF(FR.LT.FR0) THEN
         XN=SQFRH*IZZ/SQRT(FR0-FR)
         if(xn.le.tkn) then
            xkn=un
          else
            xn1=un/(xn+un)
            xkn=ckn*xn*xn1*xn1
         end if
         BETA=CB*Z3(IZZ)*XKN/(XN*XN*XN*XN)*ELEC23(ID)
         beta=beta*bergfc
         BETA3=BETA*BETA*BETA
         BETA32=SQRT(BETA3)
         F=(DWC1(IZZ,ID)*BETA3)/(UN+DWC2(ID)*BETA32)
c
c     contribution from neutral particles
c
         xn2=xn*xn+un
         xnh=0.
         xnhe1=0.
         if(ielh.gt.0) xnh=popul(nfirst(ielh),id)
         if(ielhe1.gt.0) xnhe1=popul(nfirst(ielhe1),id)
         w0=exp(wa0*xn2*xn2*xn2*(xnh+xnhe1))
         W0=1.
c
         DW1=UN-F/(UN+F)*w0
       ELSE
         DW1=UN
      END IF
      RETURN
      END