  We present a theoretical model for understanding the kinetics of a long
polymer in solution. A Smoluchowski-like equation has been used to model the
problem of polymer looping with a Dirac delta function sink of finite strength.
The results for rate constants have been obtained by using Green's function. In
this model, the rate constants for end-to-end looping of polymer exhibits
simple Arrhenius behavior. The rate constants are sensitive to relaxation time,
bond length and chain length dependence of the looping probability. In
particular, for short term rate constant, relaxation time makes loop formation
between two ends of a polymer chain slower but has a direct dependence with
long term rate constant. We also show that for shorter polymer strands looping
is slower as compared to polymer having longer chain length. The long term rate
constant shows inverse square root dependence on the length of the chain. The
bond length strongly affects the probability of loop formation as for long
constructs of polymer, the end-to-end distance is found to exhibit inverse
power law relationship to bond length. We also observe that the short term rate
constant for flexible polymer shows stronger affinity for loop formation.
