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ABSTRACT The detection of many complex organic molecules (COMs) in interstellar space has sparked the study of their origins. While the formation of COMs detected in hot cores is attributed to photochemistry on warming grain surfaces followed by recombination of radicals and desorption, the formation routes in colder regions are still a debated issue with a number of theories such as cosmic ray bombardment on interstellar ice mantles or non-diffusive surface chemistry. Here, we present another method with reactions involving metastable atomic oxygen in the O(1D) state, which is initially produced by photodissociation of oxygen-containing species in interstellar ices. As a first example, we study the reactions of metastable oxygen atoms and methane in ices to form both formaldehyde and methanol. The reaction is studied incorporating two different surface processes: diffusive and non-diffusive chemistry. The formation of methanol and formaldehyde via metastable oxygen atoms is compared with well-known formation routes of both to understand the O(1D) contributions at different temperatures.
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Formation of Complex Organic Molecules in Hot Molecular Cores through Nondiffusive Grain-surface and Ice-mantle Chemistry
Abstract A new, more comprehensive model of gas–grain chemistry in hot molecular cores is presented, in which nondiffusive reaction processes on dust-grain surfaces and in ice mantles are implemented alongside traditional diffusive surface/bulk-ice chemistry. We build on our nondiffusive treatments used for chemistry in cold sources, adopting a standard collapse/warm-up physical model for hot cores. A number of other new chemical model inputs and treatments are also explored in depth, culminating in a final model that demonstrates excellent agreement with gas-phase observational abundances for many molecules, including some (e.g., methoxymethanol) that could not be reproduced by conventional diffusive mechanisms. The observed ratios of structural isomers methyl formate, glycolaldehyde, and acetic acid are well reproduced by the models. The main temperature regimes in which various complex organic molecules (COMs) are formed are identified. Nondiffusive chemistry advances the production of many COMs to much earlier times and lower temperatures than in previous model implementations. Those species may form either as by-products of simple-ice production, or via early photochemistry within the ices while external UV photons can still penetrate. Cosmic ray-induced photochemistry is less important than in past models, although it affects some species strongly over long timescales. Another production regime occurs during the high-temperature desorption of solid water, whereby radicals trapped in the ice are released onto the grain/ice surface, where they rapidly react. Several recently proposed gas-phase COM-production mechanisms are also introduced, but they rarely dominate. New surface/ice reactions involving CH and CH2are found to contribute substantially to the formation of certain COMs.
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- Award ID(s):
- 1906489
- PAR ID:
- 10363016
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal Supplement Series
- Volume:
- 259
- Issue:
- 1
- ISSN:
- 0067-0049
- Format(s):
- Medium: X Size: Article No. 1
- Size(s):
- Article No. 1
- Sponsoring Org:
- National Science Foundation
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