Microwave spectra of molecules of astrophysical interest. XIX. methyl cyanide

Boucher, D.; Burie, J.; Bauer, A.; Dubrulle, A.; Demaison, J.

doi:10.1063/1.555625

Cited by 74 publications

(31 citation statements)

References 6 publications

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“…Menten et al 1988;Leurini et al 2004). Methyl cyanide is a well-known probe of kinetic temperature (Boucher et al 1980). But N-bearing species have a different distribution, so that temperatures derived from these molecules may thus differ from those derived from methyl formate.…”

Section: Comparison With Previous Studiesmentioning

confidence: 99%

HCOOCH₃as a probe of temperature and structure in Orion-KL

Favre

Despois

Brouillet

et al. 2011

A&A

100

238

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Context. The Orion Kleinmann-Low nebula (Orion-KL) is a complex region of star formation. Whereas its proximity allows studies on a scale of a few hundred AU, spectral confusion makes it difficult to identify molecules with low abundances. Aims. We studied an important oxygenated molecule, HCOOCH 3 , to characterize the physical conditions, temperature, and density of the different molecular source components. Methyl formate presents strong close rotational transitions covering a wide range of energy, and its emission in Orion-KL is not contaminated by the emission of N-bearing molecules. This study will help in the future 1) to constrain chemical models for the formation of methyl formate in gas phase or on grain mantles and 2) to search for more complex or prebiotic molecules. Methods. We used high-resolution observations from the IRAM Plateau de Bure Interferometer to reduce spectral confusion and to better isolate the molecular emission regions. We used twelve data sets with a spatial resolution down to 1.8 × 0.8 . Continuum emission was subtracted by selecting apparently line-free channels. Results. We identify 28 methyl formate emission peaks throughout the 50 field of observations. The two strongest peaks, named MF1 and MF2, are in the Compact Ridge and in the southwest of the Hot Core, respectively. From a comparison with single-dish observations, we estimate that we miss less than 15% of the flux and that spectral confusion is still prevailing as half of the expected transitions are blended over the region. Assuming that the transitions are thermalized, we derive the temperature at the five main emission peaks. At the MF1 position in the Compact Ridge we find a temperature of 80 K in a 1.8 × 0.8 beam size and 120 K on a larger scale (3.6 × 2.2 ), suggesting an external source of heating, whereas the temperature is about 130 K at the MF2 position on both scales. Transitions of methyl formate in its first torsionally excited state are detected as well, and the good agreement of the positions on the rotational diagrams between the ground state and the v t = 1 transitions suggests a similar temperature. The LSR velocity of the gas is between 7.5 and 8.0 km s −1 depending on the positions and column density peaks vary from 1.6 × 10 16 to 1.6 × 10 17 cm −2 . A second velocity component is observed around 9−10 km s −1 in a north-south structure stretching from the Compact Ridge up to the BN object, and this component is warmer at the MF1 peak. The two other C 2 H 4 O 2 isomers are not detected, and the derived upper limit for the column density is ≤3 × 10 14 cm −2 for glycolaldehyde and ≤2 × 10 15 cm −2 for acetic acid. From the 223 GHz continuum map, we identify several dust clumps with associated gas masses in the range 0.8 to 5.8 M . Assuming that the methyl formate is spatially distributed as the dust is, we find relative abundances of methyl formate in the range ≤0.1 × 10 −8 to 5.2 × 10 −8 . We suggest a relation between the methyl formate distribution and shocks as traced by 2.12 μm H 2 emission.

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Section: Comparison With Previous Studiesmentioning

confidence: 99%

HCOOCH₃as a probe of temperature and structure in Orion-KL

Favre

Despois

Brouillet

et al. 2011

A&A

100

238

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“…a Rest frequencies from Boucher et al (1980); a ¼ 3:922(1) from Gadhi et al (1984). b Rest frequencies from Kukolich (1972); a ¼ 3:830(60) from Ghosh et al (1953).…”

Section: Speciesmentioning

confidence: 99%

Interstellar Isomers: The Importance of Bonding Energy Differences

Remijan

Hollis

Lovas

et al. 2005

ApJ

100

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We present strong detections of methyl cyanide (CH 3 CN), vinyl cyanide (CH 2 CHCN), ethyl cyanide (CH 3 CH 2 CN), and cyanodiacetylene (HC 4 CN) molecules with the Green Bank Telescope (GBT) toward the Sgr B2(N) molecular cloud. Attempts to detect the corresponding isocyanide isomers were only successful in the case of methyl isocyanide (CH 3 NC ) for its J K ¼ 1 0 0 0 transition, which is the first interstellar report of this line. To determine the spatial distribution of CH 3 NC, we used archival Berkeley-Illinois-Maryland Association ( BIMA) array data for the J K ¼ 4 K 3 K (K ¼ 0 3) transitions, but no emission was detected. From ab initio calculations, the bonding energy difference between the cyanide and isocyanide molecules is >8500 cm À1 (>12,000 K ). Thus, cyanides are the more stable isomers and would likely be formed more preferentially over their isocyanide counterparts. That we detect CH 3 NC emission with a single antenna (Gaussian beam size B ¼ 1723 arcsec 2 ) but not with an interferometer ( B ¼ 192 arcsec 2 ) strongly suggests that CH 3 NC has a widespread spatial distribution toward the Sgr B2( N ) region. Other investigators have shown that CH 3 CN is present both in the LMH hot core of Sgr B2( N ) and in the surrounding medium, while we have shown that CH 3 NC appears to be deficient in the LMH hot core. Thus, largescale, nonthermal processes in the surrounding medium may account for the conversion of CH 3 CN to CH 3 NC, while the LMH hot core, which is dominated by thermal processes, does not produce a significant amount of CH 3 NC. Ice analog experiments by other investigators have shown that radiation bombardment of CH 3 CN can produce CH 3 NC, thus supporting our observations. We conclude that isomers separated by such large bonding energy differences are distributed in different interstellar environments, making the evaluation of column density ratios between such isomers irrelevant unless it can be independently shown that these species are cospatial.

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“…Provided that the collision rate is sufficient to thermalize the rotational levels within each K ladder, the rotational excitation temperature of CH 3 CN is equal to the gas kinetic temperature (Boucher et al 1980;Wright et al 1995). Our observation band covers the J = 12 → 11 transitions of CH 3 CN around 220 GHz, with upper state energy levels from ∼70 K to ∼500 K, yielding a wide range for determining temperatures.…”

Section: Ch 3 Cnmentioning

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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Microwave spectra of molecules of astrophysical interest. XIX. methyl cyanide

Cited by 74 publications

References 6 publications

HCOOCH₃as a probe of temperature and structure in Orion-KL

HCOOCH₃as a probe of temperature and structure in Orion-KL

Interstellar Isomers: The Importance of Bonding Energy Differences

Resolving the chemical substructure of Orion-KL

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Microwave spectra of molecules of astrophysical interest. XIX. methyl cyanide

Cited by 74 publications

References 6 publications

HCOOCH3as a probe of temperature and structure in Orion-KL

HCOOCH3as a probe of temperature and structure in Orion-KL

Interstellar Isomers: The Importance of Bonding Energy Differences

Resolving the chemical substructure of Orion-KL

Contact Info

Product

Resources

About

HCOOCH₃as a probe of temperature and structure in Orion-KL

HCOOCH₃as a probe of temperature and structure in Orion-KL