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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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Hydrogenation reactions of carbon on Earth: Linking methane, margarine, and life
Abstract Hydrogenation reactions are a major route of electron and proton flow on Earth. Interfacing geology and organic chemistry, hydrogenations occupy pivotal points in the Earth’s global geochemical cycles. Some examples of hydrogenation reactions on Earth today include the production and consumption of methane in both abiotic and biotic reactions, the reduction of protons in hydrothermal settings, and the biological synthesis and degradation of fatty acids. Hydrogenation reactions were likely important for prebiotic chemistry on the early Earth, and today serve as one of the fundamental reaction classes that enable cellular life to construct biomolecules. An understanding and awareness of hydrogenation reactions is helpful for comprehending the larger web of molecular and material inter-conversions on our planet. In this brief review we detail some important hydrogenation and dehydrogenation reactions as they relate to geology, biology, industry, and atmospheric chemistry. Such reactions have implications ranging from the suite of reactions on early Earth to industrial applications like the production of hydrocarbon fuel.
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- Award ID(s):
- 1724300
- PAR ID:
- 10155145
- Date Published:
- Journal Name:
- American Mineralogist
- Volume:
- 105
- Issue:
- 5
- ISSN:
- 0003-004X
- Page Range / eLocation ID:
- 599 to 608
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.2138/am-2020-6928CCBYNCND
