Monte Carlo simulation for the formation of interstellar grain mantle.

To mimic the exact interstellar condition, gas grain interactions via accretion from the gas phase and desorption from the grain surface are considered. Chemical composition of the grain mantle is noticed to be highly dependent on the physical parameters associated with a molecular cloud. Around the lower visual extinction (Aν ≤ 6), Interstellar photons are seen to play an important role via photo-dissociation and photo-evaporation towards the chemical composition of the interstellar grain mantle. We have studied the effects of photo-reactions by varying the number of layers which could be affected by it. Model calculations are carried out for a realistic time dependent case (i.e., extinction parameter and number density of the cloud both are changing with time) to follow the chemical evolution during the collapsing phase of a proto-star. Different routes to the formation of water molecules are extensively studied and it is noticed that around the dense region, production of water molecules via O3 and H2O2 contributes significantly. [ABSTRACT FROM AUTHOR]