2000NewA....5..441A

We have studied the chemical evolution in the central core of a contracting cloud representing W3 IRS4. We modified the equation of temperature to satisfy the physical conditions of W3 IRS4. The chemical rate equations and the hydrodynamics are integrated simultaneously. The contraction is followed from a very low density of n = 10 cm^ - 3 to high core density of n = 10^6 cm^ - 3. The chemical evolution is studied for various chemical conditions including both the effects of varying cosmic ray ionization rate and the effect of ion-dipole molecule collisions.The main results by using the more extensive chemical network with the most updating reaction rates show that the calculated fractional abundances are in agreement with observation at intermediate and enhanced cosmic ray ionization rate at high depletion of elemental atoms.