The interstellar gas-phase chemistry of HCN and HNC

Loison, Jean‐Christophe; Wakelam, Valentine; Hickson, Kevin M.

doi:10.1093/mnras/stu1089

Cited by 108 publications

(121 citation statements)

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“…Additional exchange possibilities have also been considered, such as the reaction between 15 N and C 2 N. As far as 13 C possible fractionation is concerned, we find that CN could be enriched in 13 C through the exchange reactions of CN with 13 C and 13 C + . However, such a mechanism does not hold for HNC because atomic carbon is found to react with HNC (Loison et al 2014). 13 C enrichment of HCN is also found to be unlikely since the calculated transition state lies above the entrance level in the hypothetical isomerization process (C mechanism).…”

Section: Chemical Reactions Involving Isotopicmentioning

confidence: 97%

“…HNC has recently been shown to react with atomic carbon (Loison et al 2014), which leads to the different steady state isotopic ratios obtained for HCN and HNC. The CN chemistry is then somewhat decoupled from that of HCN and HNC.…”

Section: C Chemistrymentioning

confidence: 99%

“…HCN and HNC are formed at relatively long times via CN + H 3 + → HNC + /HCN + + H 2 , followed immediately by HNC + + H 2 → HCNH + + H, giving back HCN and HNC via DR (Mendes et al 2012). With the adopted elemental abundances, the main CN destruction reactions are, however, O + CN and N + CN so that the HCNH + /HCN + /HNC + /HCN/HNC/CN network is not a closed system in contrast to models including coupled gas-grain chemistry (Loison et al 2014). …”

Section: C Chemistrymentioning

confidence: 99%

See 2 more Smart Citations

Isotopic fractionation of carbon, deuterium, and nitrogen: a full chemical study

Roueff

Loison

Hickson

2015

A&A

172

349

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Context. The increased sensitivity and high spectral resolution of millimeter telescopes allow the detection of an increasing number of isotopically substituted molecules in the interstellar medium. The 14 N/ 15 N ratio is difficult to measure directly for molecules containing carbon. Aims. Using a time-dependent gas-phase chemical model, we check the underlying hypothesis that the 13 C/ 12 C ratio of nitriles and isonitriles is equal to the elemental value. Methods. We built a chemical network that contains D, 13 C, and 15 N molecular species after a careful check of the possible fractionation reactions at work in the gas phase. Results. Model results obtained for two different physical conditions that correspond to a moderately dense cloud in an early evolutionary stage and a dense, depleted prestellar core tend to show that ammonia and its singly deuterated form are somewhat enriched in 15 N, which agrees with observations. The 14 N/ 15 N ratio in N 2 H + is found to be close to the elemental value, in contrast to previous models that obtain a significant enrichment, because we found that the fractionation reaction between 15 N and N 2 H + has a barrier in the entrance channel. The high values of the N 2 H + / 15 NNH + and N 2 H + /N 15 NH + ratios derived in L1544 cannot be reproduced in our model. Finally, we find that nitriles and isonitriles are in fact significantly depleted in 13 C, thereby challenging previous interpretations of observed C 15 N, HC 15 N, and H 15 NC abundances from 13 C containing isotopologues.

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Section: Chemical Reactions Involving Isotopicmentioning

confidence: 97%

Section: C Chemistrymentioning

confidence: 99%

Section: C Chemistrymentioning

confidence: 99%

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Isotopic fractionation of carbon, deuterium, and nitrogen: a full chemical study

Roueff

Loison

Hickson

2015

A&A

172

349

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“…A possible gas-phase formation mechanism for ethyl cyanide in the gas phase involves a radiative association reaction, followed by dissociative electron recombination, as shown in Figure 3 (Herbst 1985;Anicich 1993;Loison et al 2014). The carbon-carbon bonds in CH 3 CH 2 CN are therefore likely formed from HCN and CH 3 + and/or CH 4 + .…”

Section: Chemical Implications For Isotopic Enrichmentmentioning

confidence: 99%

The ¹²C/¹³C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry

Halfen

Woolf

Ziurys

2017

ApJ

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A study has been conducted of 12 C/ 13 C ratios in five complex molecules in the Galactic center. H 2 CS, CH 3 CCH, NH 2 CHO, CH 2 CHCN, and CH 3 CH 2 CN and their 13 C-substituted species have been observed in numerous transitions at 1, 2, and 3 mm, acquired in a spectral-line survey of Sgr B2(N), conducted with the telescopes of the Arizona Radio Observatory (ARO). Between 22 and 54 individual, unblended lines for the 12 C species and 2-54 for 13 C-substituted analogs were modeled in a global radiative transfer analysis. All five molecules were found to consistently exhibit two velocity components near V LSR ∼ 64 and 73 km s −1 , with column densities ranging from N tot ∼ 3 × 10 14 −4 × 10 17 cm −2 and ∼2 × 10 13 −1 × 10 17 cm −2 for the 12 C and 13 C species, respectively. Based on 14 different isotopic combinations, ratios were obtained in the range 12 C/ 13 C = 15±5 to 33±13, with an average value of 24±7, based on comparison of column densities. These measurements better anchor the 12 C/ 13 C ratio at the Galactic center, and suggest a slightly revised isotope gradient of 12 C/ 13 C = 5.21(0.52) D GC + 22.6(3.3). As indicated by the column densities, no preferential 13 C enrichment was found on the differing carbon sites of CH 3 CCH, CH 2 CHCN, and CH 3 CH 2 CN. Because of the elevated temperatures in Sgr B2(N), 13 C isotopic substitution is effectively "scrambled," diminishing chemical fractionation effects. The resulting ratios thus reflect stellar nucleosynthesis and Galactic chemical evolution, as is likely the case for most warm clouds.

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“…The most recent, state-of-the-art chemical modeling study of isotope fractionation was conducted by Roueff et al (2015) Loison et al 2014), which couples HCN back into the chemical network post-production, allowing it to be fractionated at any time that the 13 C pool is depleted. In addition, Roueff et al (2015) use an updated ΔE/k B for Equation (2) of 17 K, c.f.…”

Section: Chemical Modeling and Isotopologue Ratiosmentioning

confidence: 99%

Modeling the Molecular Gas in NGC 6240

Tunnard

Greve

García‐Burillo

et al. 2015

ApJ

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We present the first observations of H 13 CN 1 0 ( ) -, H 13 CO + 1 0 ( ) -, and SiO 2 1 ( ) -in NGC 6240, obtained with the IRAM Plateau de Bure Interferometer. Combining a Markov Chain Monte Carlo code with Large Velocity Gradient (LVG) modeling, and with additional data from the literature, we simultaneously fit three gas phases and six molecular species to constrain the physical condition of the molecular gas, including mass−luminosity conversion factors. We find M 10 10  of dense molecular gas in cold, dense clouds (T 10 k~K , n 10 ) which we attribute to isotope fractionation in the cold, dense clouds.

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The interstellar gas-phase chemistry of HCN and HNC

Cited by 108 publications

References 110 publications

Isotopic fractionation of carbon, deuterium, and nitrogen: a full chemical study

Isotopic fractionation of carbon, deuterium, and nitrogen: a full chemical study

The ¹²C/¹³C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry

Modeling the Molecular Gas in NGC 6240

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The interstellar gas-phase chemistry of HCN and HNC

Cited by 108 publications

References 110 publications

Isotopic fractionation of carbon, deuterium, and nitrogen: a full chemical study

Isotopic fractionation of carbon, deuterium, and nitrogen: a full chemical study

The 12C/13C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry

Modeling the Molecular Gas in NGC 6240

Contact Info

Product

Resources

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The ¹²C/¹³C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry