Dehydrogenation effects on the stability of aromatic units in polycyclic aromatic hydrocarbons in the interstellar medium: A computational study at finite temperature

Parneix, P.; Gamboa, Antonio; Falvo, Cyril; Bonnin, M.A.; Pino, T.; Calvo, F.

doi:10.1016/j.molap.2017.05.001

Cited by 13 publications

(14 citation statements)

References 51 publications

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“…Another example concerns the sequence proposed in Figure 3. Recent quantum chemical calculations performed by Parneix et al (2017) suggest that the formation of pentagonal defects which provides curvature and can lead to folding may in fact occur before dehydrogenation (contrary to what is depicted in the scenario of Fig. 3).…”

Section: Building a Photo-physical Model Of The Evolution Of Large Camentioning

confidence: 87%

Observations of the photochemical evolution of carbonaceous macromolecules in star-forming regions

Berné

2019

Proc. IAU

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The goal of this contribution is to illustrate how spatially resolved spectroscopic observations of the infrared emission of UV irradiated regions, from star forming regions to the diffuse ISM, can be used to rationalize the chemical evolution of carbonaceous macromolecules in space, with the help of astrophysical models. For instance, observations with the Spitzer space telescope lead to the idea that fullerenes (including C60 can form top-down from Polycyclic Aromatic Hydrocarbons in the interstellar medium. The possibility that this process can occur in space was tested using a photochemical model which includes the key molecular parameters derived from experimental and theoretical studies. This approach allows to test the likelihood that the proposed path is realistic, but, more importantly, it allows to isolate the key physical processes and parameters that are required to capture correctly the evolution of carbonaceous molecules in space. In this specific case, we found that relaxation through thermally excited electronic states (a physical mechanism that is largely unexplored, except by few a teams) is one of the keys to model the photochemistry of the considered species. Subsequent quantum chemical studies stimulated by the (limited) astrophysical model showed that a detailed mapping of the energetics of isomerization and de-hydrogenation is necessary to understand the competition between these processes in space.Such approaches, involving experimentalists and theoreticians, are particularly promising in the context of the upcoming JWST mission, which will provide access to the signatures of carbonaceous species in emission and in absorption at an angular resolution that will enable to reach new chemical frontiers in star and even in planet forming regions.

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Section: Building a Photo-physical Model Of The Evolution Of Large Camentioning

confidence: 87%

Observations of the photochemical evolution of carbonaceous macromolecules in star-forming regions

Berné

2019

Proc. IAU

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“…9) provides a computationallyefficient tool to investigate photo-induces fragmentation and isomerization; not only does it compare successfully with experimental results, it also gives energetics comparable to standard DFT [280]. Alternatively, isomerization pathways and equilibrium properties at fixed total energy in the canonical or microcanonical ensembles can be described using biased Monte-Carlo methods [289]. Potential energy of specific molecular configurations are determined using a reactive force field, such as AIREBO, which includes also the effects of anharmonicity, and the thermodynamical properties are evaluated through the Wang-Landau approach; this approach consists in random walk around the configurations that is quickly able to visit all the available states and build an estimate of the density of configurational states.…”

Section: Challenges and New Directionsmentioning

confidence: 98%

Roadmap on dynamics of molecules and clusters in the gas phase

et al. 2021

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This roadmap article highlights recent advances, challenges and future prospects in studies of the dynamics of molecules and clusters in the gas phase. It comprises nineteen contributions by scientists with leading expertise in complementary experimental and theoretical techniques to probe the dynamics on timescales spanning twenty order of magnitudes, from attoseconds to minutes and beyond, and for systems ranging in complexity from the smallest (diatomic) molecules to clusters and nanoparticles. Combining some of these techniques opens up new avenues to unravel hitherto unexplored reaction pathways and mechanisms, and to establish their significance in, e.g. radiotherapy and radiation damage on the nanoscale, astrophysics, astrochemistry and atmospheric science. Graphic abstract

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“…When heated to about 1000 K by the absorption of a ∼10 eV photon, it immediately reorganizes into a more stable form with some general salient features, such as edge reorganization into a (5,7) rather than a (6,6) carbon pattern, or presence of at least one inner pentagon inducing a curved structure, such as corannulene. Although it is probable that such structures do appear before the end of the total dehydrogenation (Parneix et al 2017), this should not change the subsequent evolution of the flake much if it eventually becomes completely dehydrogenated. Nothing in these features should significantly change from N C = 60 to N C = 40.…”

Section: Cage Formation From Carbon Nanoflakesmentioning

confidence: 99%

Intermediate-size fullerenes as degradation products of interstellar polycyclic aromatic hydrocarbons

Omont

Bettinger

2021

A&A

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The high interstellar abundances of polycyclic aromatic hydrocarbons (PAHs) and their size distribution are the result of complex chemical processes implying dust, UV radiation, and the main gaseous components (H, C+, and O). These processes must explain the high abundance of relatively small PAHs in the diffuse interstellar medium (ISM) and imply the continuous formation of some PAHs that are small enough (number of carbon atoms NC < ~35–50) to be completely dehydrogenated by interstellar UV radiation. The carbon clusters Cn thus formed are constantly exposed to the absorption of ~10–13.6 eV UV photons, allowing isomerization and favoring the formation of the most stable isomers. They might tend to form irregular carbon cages. The frequent accretion of interstellar C+ ions could favor further cage isomerization, as is known in the laboratory for C60, possibly yielding most stable fullerenes, such as C40, C44, and C50. These fullerenes are expected to be very stable in the diffuse ISM because C2 ejection is not possible by single UV photon absorption, but could need rare two-photon absorption. It is possible that at least one of these fullerenes or its cation is as abundant as C60 or C60+ in the diffuse ISM, although this abundance is limited by the lack of observed matching features in observed mid-infrared spectra. B3LYP calculations of the visible spectrum for a number of fullerene isomers with 40 ≤NC ≤ 50 show that they generally have a few spectral bands in the visible range, with f-values in the range of a few 10−2. This could make such fullerenes interesting candidates for the carriers of some diffuse interstellar bands.

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Dehydrogenation effects on the stability of aromatic units in polycyclic aromatic hydrocarbons in the interstellar medium: A computational study at finite temperature

Cited by 13 publications

References 51 publications

Observations of the photochemical evolution of carbonaceous macromolecules in star-forming regions

Observations of the photochemical evolution of carbonaceous macromolecules in star-forming regions

Roadmap on dynamics of molecules and clusters in the gas phase

Intermediate-size fullerenes as degradation products of interstellar polycyclic aromatic hydrocarbons

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