REASSESSMENT OF THE DISSOCIATIVE RECOMBINATION OF N<sub>2</sub>H<sup>+</sup>AT CRYRING

Vigren, Erik; Zhaunerchyk, V.; Hamberg, Mathias; Kamińska, Magdalena; Semaniak, J.; Ugglas, M. af; Larsson, Mats; Thomas, Richard; Geppert, Wolf D.

doi:10.1088/0004-637x/757/1/34

Cited by 39 publications

(46 citation statements)

References 24 publications

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“…formed from the dissociative recombination (DR) of N 2 H + , a reaction that has been recently revisited by Vigren et al (2012), who derive a branching ratio towards a NH of 7%. We checked that this analysis still holds for model (b) even if the reaction of N 2 H + with CO becomes more efficient.…”

Section: Nitrogen Hydridesmentioning

confidence: 99%

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

Roueff

Loison

Hickson

2015

A&A

171

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: Nitrogen Hydridesmentioning

confidence: 99%

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

Roueff

Loison

Hickson

2015

A&A

171

349

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“…The most important changes regard the dissociative recombinations of ions such as NH + 2 , NH + 3 , and NH + 4 , which are critical (Milam et al 2005). for the production of hydrides. Following Dislaire et al (2012), the dissociative recombination of N 2 H + possesses a channel producing NH with a branching ratio of ≈ 5% (Vigren et al 2012). The gas phase ortho-to-para conversion of H 2 through proton exchange reactions has also been fully updated (Rist et al 2013, and references therein) since the rate of the key reaction N + + H 2 depends critically on the ortho-to-para ratio of H 2 (Dislaire et al 2012).…”

Section: Model Calculationsmentioning

confidence: 99%

The CN/C¹⁵N isotopic ratio towards dark clouds

Hily-Blant

Forêts

Fauré

et al. 2013

A&A

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Understanding the origin of the composition of solar system cosmomaterials is a central question, not only in the cosmochemistry and astrochemistry fields, and requires various approaches to be combined. Measurements of isotopic ratios in cometary materials provide strong constraints on the content of the protosolar nebula. Their relation with the composition of the parental dark clouds is, however, still very elusive. In this paper, we bring new constraints based on the isotopic composition of nitrogen in dark clouds, with the aim of understanding the chemical processes that are responsible for the observed isotopic ratios. We have observed and detected the fundamental rotational transition of C 15 N towards two starless dark clouds, L1544 and L1498. We were able to derive the column density ratio of C 15 N over 13 CN towards the same clouds, and obtain the CN/C 15 N isotopic ratios, which were found to be 500 ± 75 for both L1544 and L1498. These values are therefore marginally consistent with the protosolar value of 441. Moreover, this ratio is larger than the isotopic ratio of nitrogen measured in HCN. In addition, we present model calculations of the chemical fractionation of nitrogen in dark clouds, which make it possible to understand how CN can be deprived of 15 N and HCN can simultaneously be enriched in heavy nitrogen. The non-fractionation of N 2 H + , however, remains an open issue and we propose some chemical way of alleviating the discrepancy between model predictions and the observed ratios.

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“…We have also updated the rates for the neutralneutral reactions that lead to production of N 2 (see Table 3 from Le Gal et al 2013, and references therein). Finally, we have updated the branching ratio of the N 2 H + dissociative recombination (Vigren et al 2012). The left panel of Fig.…”

Section: Appendix A: Model Predictions For the Nitrogen Chemistrymentioning

confidence: 99%

Chemical modeling of the L1498 and L1517B prestellar cores: CO and HCO⁺depletion

Maret

Bergin

Tafalla

2013

A&A

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Prestellar cores exhibit a strong chemical differentiation, which is mainly caused by the freeze-out of molecules onto the grain surfaces. Understanding this chemical structure is important, because molecular lines are often used as probes to constrain the core physical properties. Here we present new observations and analysis of the C 18 O (1-0) and H 13 CO + (1-0) line emission in the L1498 and L1517B prestellar cores, located in the Taurus-Auriga molecular complex. We model these observations with a detailed chemistry network coupled to a radiative transfer code. Our model successfully reproduces the observed C 18 O (1-0) emission for a chemical age of a few 10 5 years. On the other hand, the observed H 13 CO + (1-0) is reproduced only if cosmic-ray desorption by secondary photons is included, and if the grains have grown to a bigger size than average ISM grains in the core interior. This grain growth is consistent with the infrared scattered light ("coreshine") detected in these two objects, and is found to increase the CO abundance in the core interior by about a factor four. According to our model, CO is depleted by about 2-3 orders of magnitude in the core center.

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REASSESSMENT OF THE DISSOCIATIVE RECOMBINATION OF N₂H⁺AT CRYRING

Cited by 39 publications

References 24 publications

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

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

The CN/C¹⁵N isotopic ratio towards dark clouds

Chemical modeling of the L1498 and L1517B prestellar cores: CO and HCO⁺depletion

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REASSESSMENT OF THE DISSOCIATIVE RECOMBINATION OF N2H+AT CRYRING

Cited by 39 publications

References 24 publications

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

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

The CN/C15N isotopic ratio towards dark clouds

Chemical modeling of the L1498 and L1517B prestellar cores: CO and HCO+depletion

Contact Info

Product

Resources

About

REASSESSMENT OF THE DISSOCIATIVE RECOMBINATION OF N₂H⁺AT CRYRING

The CN/C¹⁵N isotopic ratio towards dark clouds

Chemical modeling of the L1498 and L1517B prestellar cores: CO and HCO⁺depletion