SIMBAD references

We have investigated the effect of using real and pseudo time dependent models on the chemical evolution of collapsing interstellar clouds considering, as a first step, the early free-fall collapse phase. Two chemical models have been presented in all cases: 1) pure gas phase chemistry; 2) combined dust/gas chemistry in which solid grain chemistry is considered simultaneously with the gas. Accretion, explosive desorption, surface reactions and photochemical processing are the main additional processes involved in the model of dust/gas interactions relative to pure gas phase processes. The differences in this early stage of a collapsing interstellar cloud resulting from real and pseudo time dependent models in both pure gas phase and dust/gas models are small for low mass (1M_☉). For a high mass (10M_☉) cloud in which its free-fall collapse starts from lower density and evolves to higher density with longer time of chemical evolution the use of real time dependence becomes important. We found, as expected, a clear difference between using pure gas phase and combined dust/gas models both in pseudo and real time dependent models. This result confirms the important role of dust/gas interactions not only in chemical models of quiescent clouds but also for collapsing interstellar clouds. Our dust/gas models which include explicitly the gas dust interactions and start with normal depleted atomic abundances can give an alternative scenario to the so-called "cyclic-dynamical chemical model" which appears to be required by another chemical evolution model of collapsing clouds. The justification and relevance of initial elemental and molecular abundances are discussed in relation to the collapsing cloud models.