Water formation in early solar nebula: I. Quasi-stationary cloud core

It is shown that in the dust phase about 106 to 107 times more water is produced than in the gas phase. Further, the total mass of the water formed in the core varies only marginally between 0.11 and 0.12 wt% for a life time of the core between 1 and 6.5 Mega years, respectively. Roughly 84% of the oxygen atoms are incorporated into water molecules, if the intensity of the radiation field is about 1 Habing. The number of oxygen atoms decreases to 77% if this intensity triples. The water amount produced in the gas phase depends stronger on the interstellar radiation field and the living time of the core than the water amount formed on dust. For the 1 Habing radiation intensity the size distribution of the dust grains has nearly no influence. Finally, a number of species representing compounds mainly formed in the dust or in the gas phase was selected (H2O, CO, etc.) in order to use them for a validation of our model. Thereto, we have compared the abundances of these compounds simulated with the model to the related data from observations published in the literature. For almost all cases except N2H+ a sufficient agreement was found.