On the Abundance Gradients of Organic Molecules along the TMC‐1 Ridge

Markwick, A. J.; Millar, T. J.; Charnley, Steven B.

doi:10.1086/308814

Cited by 104 publications

(123 citation statements)

References 35 publications

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“…Using the old data, the model predicted a methanol peak abundance relative to H 2 of 1 Â 10 À9 , which is in good agreement with the observations of Friberg et al, 36 which yielded a methanol abundance in the low digits of 10 À9 for TMC-1. 2,35 With the present rate coefficient and branching ratios of the DR of protonated methanol, the peak abundance is lowered to a value of 8 Â 10 À11 while that for the steady state sinks from 3 Â 10 À10 to 2 Â 10 À11 . If the recently measured rate coefficient for the radiative association of CH 3 + and H 2 O 18 is also included, the peak abundance is further diminished to 7 Â 10 À13 and the steady state to 1 Â 10 À13 , which is definitely below the observed values in dark clouds and probably below the detection limits for existing telescopes (see Fig.…”

Section: Astrophysical Implicationsmentioning

confidence: 88%

“…Therefore, the new data on the rate coefficient and the branching ratios on DR of CD 3 OD 2 + was used as an input for a model calculation of a dark cloud resembling TMC-1 using the UMIST code. 35 The branching ratios of the deuterated isotopomer were used because of the higher certainty of the data due to the lower presence of detection losses of light particles. Using the old data, the model predicted a methanol peak abundance relative to H 2 of 1 Â 10 À9 , which is in good agreement with the observations of Friberg et al, 36 which yielded a methanol abundance in the low digits of 10 À9 for TMC-1.…”

Section: Astrophysical Implicationsmentioning

confidence: 99%

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Dissociative recombination of protonated methanol

et al. 2006

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The branching ratios of the different reaction pathways and the overall rate coefficients of the dissociative recombination reactions of CH 3 OH 2 + and CD 3 OD 2 + have been measured at the CRYRING storage ring located in Stockholm, Sweden. Analysis of the data yielded the result that formation of methanol or deuterated methanol accounted for only 3 and 6% of the total rate in CH 3 OH 2 + and CD 3 OD 2 + , respectively. Dissociative recombination of both isotopomeres mainly involves fragmentation of the C-O bond, the major process being the three-body break-up forming CH 3 , OH and H (CD 3 , OD and D). The overall cross sections are best fitted by s = 1.2 AE 0.1 Â 10 À15 E À1.15AE0.02 cm 2 and s = 9.6 AE 0.9 Â 10 À16 E À1.20AE0.02 cm 2 for CH 3 OH 2 + and CD 3 OD 2 + , respectively. From these values thermal reaction rate coefficients of k(T) = 8.9 AE 0.9 Â 10 À7 (T/300) À0.59AE0.02 cm 3 s À1 (CH 3 OH 2 + ) and k(T) = 9.1 AE 0.9 Â 10 À7 (T/300) À0.63AE0.02 cm 3 s À1 (CD 3 OD 2 + ) can be calculated. A non-negligible formation of interstellar methanol by the previously proposed mechanism via radiative association of CH 3 + and H 2 O and subsequent dissociative recombination of the resulting CH 3 OH 2 + ion to yield methanol and hydrogen atoms is therefore very unlikely.

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Section: Astrophysical Implicationsmentioning

confidence: 88%

Section: Astrophysical Implicationsmentioning

confidence: 99%

Dissociative recombination of protonated methanol

et al. 2006

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“…Cometary ices are also known to be rich in ethane (24), where the observed abundances are comparable to that of methane. It is therefore plausible that large quantities of ethane can be released into the gas phase in interstellar clouds following events that result in ice mantle sublimation via graingrain collisions (25) or shocking of the ISM (26). This situation is very different from the hot core model, where a newly formed star thermally heats the grains thus leading to a thermal sublimation of the molecules from the grain (27).…”

Section: Discussionmentioning

confidence: 99%

Formation of benzene in the interstellar medium

Jones

Zhang

Kaiser

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

153

182

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Polycyclic aromatic hydrocarbons and related species have been suggested to play a key role in the astrochemical evolution of the interstellar medium, but the formation mechanism of even their simplest building block—the aromatic benzene molecule—has remained elusive for decades. Here we demonstrate in crossed molecular beam experiments combined with electronic structure and statistical calculations that benzene (C 6 H 6 ) can be synthesized via the barrierless, exoergic reaction of the ethynyl radical and 1,3-butadiene, C 2 H + H 2 CCHCHCH 2 → C 6 H 6 + H, under single collision conditions. This reaction portrays the simplest representative of a reaction class in which aromatic molecules with a benzene core can be formed from acyclic precursors via barrierless reactions of ethynyl radicals with substituted 1,3-butadiene molecules. Unique gas-grain astrochemical models imply that this low-temperature route controls the synthesis of the very first aromatic ring from acyclic precursors in cold molecular clouds, such as in the Taurus Molecular Cloud. Rapid, subsequent barrierless reactions of benzene with ethynyl radicals can lead to naphthalene-like structures thus effectively propagating the ethynyl-radical mediated formation of aromatic molecules in the interstellar medium.

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“…The favoured model of hot molecular core chemistry so far is the gas-grain model, where frozen radicals, partly produced by photolysis, become mobile during the warm-up phase, and their reactions produce COMs (Markwick et al 2000;Garrod et al 2008). Three phases are usually modelled, the cold, warm-up, and hot molecular core stages.…”

Section: Chemistry In the Hot Molecular Corementioning

confidence: 99%

Resolving the chemical substructure of Orion-KL

Feng

Beuther

Henning

et al. 2015

A&A

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Context. The Kleinmann-Low nebula in Orion (Orion-KL) is the nearest example of a high-mass star-forming environment. Studying the resolved chemical substructures of this complex region provides important insight into the chemistry of high-mass star-forming regions (HMSFRs), as it relates to their evolutionary states. Aims. The goal of this work is to resolve the molecular line emission from individual substructures of Orion-KL at high spectral and spatial resolution and to infer the chemical properties of the associated gas.Methods. We present a line survey of Orion-KL obtained from combined Submillimeter Array (SMA) interferometric and IRAM 30 m single-dish observations. Covering a 4 GHz bandwidth in total, this survey contains over 160 emission lines from 20 species (25 isotopologues), including 11 complex organic molecules (COMs). Spectra are extracted from individual substructures and the intensity-integrated distribution map for each species is provided. We then estimate the rotation temperature for each substructure, along with their molecular column densities and abundances. Results. For the first time, we complement 1.3 mm interferometric data with single-dish observations of the Orion-KL region and study small-scale chemical variations in this region. (1) We resolve continuum substructures on ∼3 angular scale. (2) We identify lines from the low-abundance COMs CH 3 COCH 3 and CH 3 CH 2 OH, as well as tentatively detect CH 3 CHO and long carbon-chain molecules C 6 H and HC 7 N. (3) We find that while most COMs are segregated by type, peaking either towards the hotcore (e.g., nitrogenbearing species) or the compact ridge (e.g., oxygen-bearing species like HCOOCH 3 and CH 3 OCH 3 ), the distributions of others do not follow this segregated structure (e.g., CH 3 CH 2 OH, CH 3 OH, CH 3 COCH 3 ). (4) We find a second velocity component of HNCO, SO 2 , 34 SO 2 , and SO lines, which may be associated with a strong shock event in the low-velocity outflow. (5) Temperatures and molecular abundances show large gradients between central condensations and the outflow regions, illustrating a transition between hot molecular core and shock-chemistry dominated regimes. Conclusions. Our observations of spatially resolved abundance variations in Orion-KL provide the nearest reference source for hot molecular core and outflow chemistry, which will be an important example for interpreting the chemistry of more distant HMSFRs.

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On the Abundance Gradients of Organic Molecules along the TMC‐1 Ridge

Cited by 104 publications

References 35 publications

Dissociative recombination of protonated methanol

Dissociative recombination of protonated methanol

Formation of benzene in the interstellar medium

Resolving the chemical substructure of Orion-KL

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