A Unified Monte Carlo Treatment of Gas-Grain Chemistry for Large Reaction Networks. II. A Multiphase Gas-surface-layered Bulk Model
Abstract
The observed gas-phase molecular inventory of hot cores is believed to be significantly impacted by the products of chemistry in interstellar ices. In this study, we report the construction of a full macroscopic Monte Carlo model of both the gas-phase chemistry and the chemistry occurring in the icy mantles of interstellar grains. Our model treats icy grain mantles in a layer-by-layer manner, which incorporates laboratory data on ice desorption correctly. The ice treatment includes a distinction between a reactive ice surface and an inert bulk. The treatment also distinguishes between zeroth- and first-order desorption, and includes the entrapment of volatile species in more refractory ice mantles. We apply the model to the investigation of the chemistry in hot cores, in which a thick ice mantle built up during the previous cold phase of protostellar evolution undergoes surface reactions and is eventually evaporated. For the first time, the impact of a detailed multilayer approach to grain mantle formation on the warm-up chemistry is explored. The use of a multilayer ice structure has a mixed impact on the abundances of organic species formed during the warm-up phase. For example, the abundance of gaseous HCOOCH3 is lower in the multilayer model than in previous grain models that do not distinguish between layers (so-called two phase models). Other gaseous organic species formed in the warm-up phase are affected slightly. Finally, we find that the entrapment of volatile species in water ice can explain the two-jump behavior of H2CO previously found in observations of protostars.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2013
- DOI:
- 10.1088/0004-637X/762/2/86
- arXiv:
- arXiv:1211.3025
- Bibcode:
- 2013ApJ...762...86V
- Keywords:
-
- astrochemistry;
- ISM: abundances;
- ISM: clouds;
- stars: formation;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 50 pages, 14 figures, accepted to ApJ