Grain surface chemistry in proto-stellar star forming regions

The evolution of a star forming core from dark core to protostar spans a wide range of temperature, density, and infall dynamics. While this process is well-studied, direct observation is often difficult. Chemical evolution during this phase has the capacity to encode the history of gas and dust parcels during this phase, with the potential to leave that record in cometary ices. The combined gas-phase and grain-surface chemical evolution of over 10,000 gas+dust parcels during the star formation process. The chemical model contains 668 gas-phase and grain-surface species, and over 7000 gas-phase and over 2000 grain-surface reactions. The chemistry is first evolved in a simulated dark-core phase from an initial atomic cloud composed solely of solar abundances of H, He, C, N, O, S, Si, P, Na, Mg, Fe, F, Cl. The pre-collapse phase is evolved at 10K and n = 10^4, with the results used as initial conditions for the collapse phase chemistry. It is found that

1. Gas-phase abundances of simple molecules are primarily affected by heating of the envelope above the sublimation temperature. These results, such as for H2O, are consistent with observations.

2. Significant gas-phase complexity is achieved due to the time spent in grain surface as the grains infall into the warming envelope, and due to the high temperatures and densities in the gas phase during the infall as well.

3. A comparison of the results at theinner edge of the spherical envelope (2000AU) are surprisingly consistent with observations of cometary abundances in the solar system. This is suggestive of the possibility that a significant amount of chemical evolution in proto-planetary nebulae may be due to chemical evolution during the protostellar infall phase.

4. A potential sulphur resevoir is identified