Experimental investigation of nitrile formation from VUV photochemistry of interstellar ices analogs: acetonitrile and amino acetonitrile

Danger, Grégoire; Bossa, Jean-Baptiste; Marcellus, Pierre de; Borget, Fabien; Duvernay, Fabrice; Theulé, Patrice; Chiavassa, Thierry; d’Hendecourt, Louis Le Sergeant

doi:10.1051/0004-6361/201015736

Cited by 57 publications

(45 citation statements)

References 47 publications

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“…Danger et al (2011) have studied the formation of CH 3 CN by the UV photolysis of ethylamine (CH 3 CH 3 NH 2 ) ices. They determined that methyl cyanide could be formed at 20 K with a yield of 4%.…”

Section: Ch 3 Cn and Ch 3 Nc Chemistrymentioning

confidence: 99%

The IRAM-30 m line survey of the Horsehead PDR

Gratier

Pety

Guzmán

et al. 2013

A&A

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Context. Complex (iso-)nitrile molecules, such as CH 3 CN and HC 3 N, are relatively easily detected in our Galaxy and in other galaxies. Aims. We aim at constraining their chemistry through observations of two positions in the Horsehead edge: the photo-dissociation region (PDR) and the dense, cold, and UV-shielded core just behind it. Methods. We systematically searched for lines of CH 3 CN, HC 3 N, C 3 N, and some of their isomers in our sensitive unbiased line survey at 3, 2, and 1 mm. We stacked the lines of C 3 N to improve the detectability of this species. We derived column densities and abundances through Bayesian analysis using a large velocity gradient radiative transfer model. Results. We report the first clear detection of CH 3 NC at millimeter wavelength. We detected 17 lines of CH 3 CN at the PDR and 6 at the dense core position, and we resolved its hyperfine structure for 3 lines. We detected 4 lines of HC 3 N, and C 3 N is clearly detected at the PDR position. We computed new electron collisional rate coefficients for CH 3 CN, and we found that including electron excitation reduces the derived column density by 40% at the PDR position, where the electron density is 1-5 cm −3 . While CH 3 CN is 30 times more abundant in the PDR (2.5 × 10 −10 ) than in the dense core (8 × 10 −12 ), HC 3 N has similar abundance at both positions (8 × 10 −12 ). The isomeric ratio CH 3 NC/CH 3 CN is 0.15 ± 0.02. Conclusions. The significant amount of complex (iso-)nitrile molecule in the UV illuminated gas is puzzling as the photodissociation is expected to be efficient. This is all the more surprising in the case of CH 3 CN, which is 30 times more abundant in the PDR than in the dense core. In this case, pure gas phase chemistry cannot reproduce the amount of CH 3 CN observed in the UV-illuminated gas. We propose that CH 3 CN gas phase abundance is enhanced when ice mantles of grains are destroyed through photo-desorption or thermal-evaporation in PDRs, and through sputtering in shocks.

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Section: Ch 3 Cn and Ch 3 Nc Chemistrymentioning

confidence: 99%

The IRAM-30 m line survey of the Horsehead PDR

Gratier

Pety

Guzmán

et al. 2013

A&A

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“…The high acetonitrile can be explained by a higher photodesorption rate and a lower ice photolysis rate than those currently assumed in the models (Gratier et al 2013;Ligterink et al 2015). The Bernstein et al (2004) results on a slower photolysis process for solid CH 3 CN than for other organic molecules argue in this sense as do those of Danger et al (2011) concerning CH 3 CN formation by UV photolysis of ethylamine (CH 3 CH 2 NH 2 ) in ices. Gratier et al (2013) also highlighted the fact that the species has also been observed in shocks (Arce et al 2008;Codella et al 2009) indicating that acetonitrile might be subject to sputtering in those regions.…”

Section: Nitrile Casementioning

confidence: 84%

A new study of the chemical structure of the Horsehead nebula: the influence of grain-surface chemistry

Gal

Herbst

Dufour

et al. 2017

A&A

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A wide variety of molecules have recently been detected in the Horsehead nebula photodissociation region (PDR) suggesting that: (i) gas-phase and grain chemistries should both contribute to the formation of organic molecules, and (ii) far-ultraviolet (FUV) photodesorption may explain the release into the gas phase of grain surface species. In order to tackle these specific problems and more generally in order to better constrain the chemical structure of these types of environments we present a study of the Horsehead nebula gas-grain chemistry. To do so we used the 1D astrochemical gas-grain code Nautilus with an appropriate physical structure computed with the Meudon PDR Code and compared our modeled outcomes with published observations and with previously modeled results when available. The use of a large set of chemical reactions coupled with the time-dependent code Nautilus allows us to reproduce most of the observations well, including those of the first detections in a PDR of the organic molecules HCOOH, CH 2 CO, CH 3 CHO and CH 3 CCH, which are mostly associated with hot cores. We also provide some abundance predictions for other molecules of interest. Understanding the chemistry behind the detection of these organic molecules is crucial to better constrain the environments these molecules can probe.

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“…Besides, the most complex molecules detected nowadays such as aminoacetonitrile observed in Sgr B2 [27], a precursor of glycine, cannot be accounted for by any gas phase reactions network but supposes that the molecule has evaporated from grain surfaces. A route for aminoacetonitrile formation has recently been proposed using icy grains bulk reactions driven by UV photon photochemistry [28,29]. This last example may not necessarily be seen as the only pathway mechanism for this molecule but it just illustrates one of the capabilities of the presence of grain surfaces to obtain very different and much more complex molecules.…”

Section: Gas Phase Chemistrymentioning

confidence: 99%

Molecular complexity in astrophysical environments: From astrochemistry to “astrobiology”?

d’Hendecourt

2011

EPJ Web of Conferences

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A prebiotic molecule does not exist per-se, but only in a precise environmental contextAbstract. I present in this paper my own view about the intricate problem between the evolution of molecular complexity as observed from an astrophysicist point of view and its possible relation to the problem of the origin of life as we know it on Earth. Using arguments from observational astrophysics, I propose that life cannot really be based on other elements that the ones organizing our own so that other life forms based on totally different elemental and molecular processes are highly improbable. As a consequence terrestrial-type environments are probably the most favorable ones to life's "emergence" and subsequent evolution. Discussing molecular (organic) complexity, I show where this molecular complexity is located in astrophysical environments, mostly within inter/circumstellar solid state materials known as "grains" which, at least partly, end up in comets and asteroids and finally on planetary surfaces as meteorites. Considerations based on non directed laboratory simulations experiments, recent results regarding chiral asymmetry in potentially prebiotic matter and the possible explanation to the determinism about the choice of the L sign of the enantiomeric excesses in meteoritic amino acids, following a plausible astrophysical scenario, lead to the idea that the origin of life on Earth was indeed the result of a rather deterministic phenomenon, albeit difficult if not impossible to apprehend in its intimate mechanisms via a complete understanding of all the processes involved. Finally, the crucial point in supporting the idea of life's ubiquity and wide distribution in our Galaxy (or universe?) lies in the fact that planetary evolution, another astrophysical argument, is a major and very strong constraint for the development of life above its "minimal definition". Life, particularly the complex and evolved one, could be indeed very rare in our Galaxy, although the very large number of exoplanets may be a counter-argument to this statement. However, the deterministic nature of the processes at the origin of life on Earth, the only example we know, together with the progressively increased knowledge of the early conditions on telluric (exo)-planets and in particular those on our primitive Earth, where life did indeed appear, may render possible, in a near future, a semi-quantitative estimate of its occurrence in our Galaxy as well as major improvements in the field of prebiotic chemistry, possibly linked to the one of astrochemistry.

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Experimental investigation of nitrile formation from VUV photochemistry of interstellar ices analogs: acetonitrile and amino acetonitrile

Cited by 57 publications

References 47 publications

The IRAM-30 m line survey of the Horsehead PDR

The IRAM-30 m line survey of the Horsehead PDR

A new study of the chemical structure of the Horsehead nebula: the influence of grain-surface chemistry

Molecular complexity in astrophysical environments: From astrochemistry to “astrobiology”?

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