Based on the Wilemski-Fixman approach (J. Chem. Phys. 60, 866 (1974)) we
showed that for a flexible chain in theta solvent hydrodynamic interaction
treated with an pre-averaging approximation makes ring closing faster if the
chain is not very short. Only for a very short chain the ring closing is slower
with hydrodynamic interaction on. We have also shown that the ring closing time
for a chain with hydrodynamic interaction in theta solvent scales with the
chain length (N) as N^(1.527), in good agreement with previous renormalization
group calculation based prediction by Freidman et al. (Phys. Rev. A. 40, 5950
(1989))
