Molecular growth upon ionization of van der Waals clusters containing HCCH and HCN is a pathway to prebiotic molecules

Stein, Tamar; Bera, Partha P.; Lee, Timothy J.; Head‐Gordon, Martin

doi:10.1039/d0cp03350b

Cited by 10 publications

(13 citation statements)

References 63 publications

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“…To understand the intra-cluster ionization process at the molecular level, several studies performed ab-initio molecular dynamics (AIMD) simulations modeling different neutral cluster compositions. In agreement with experimental work, AIMD simulations have demonstrated that the molecular growth process occurs and that covalently bonded structures are formed [ 38 , 41 , 42 , 43 ]. It has been shown that, upon ionization, part of the cluster forms covalently bonded core structures, while the remaining molecules serve as spectators of the process.…”

Section: Introductionsupporting

confidence: 76%

“…In the remaining ~2.7% of the trajectories, we observed the aggregation of four acetylene molecules to yield bonded C 8 H 8 + . While other cluster compositions (namely, mixed acetylene with HCN and cyanoacetylene) enable bonding between four units [ 41 , 43 ], C 8 H 8 + species were not obtained from the acetylene hexamers previously studied, clearly demonstrating that more than six acetylene units are required to observe aggregation beyond C 6 structures from a pure acetylene cluster [ 38 , 42 ]. Again, this emphasizes the role of the cluster environment not only in the stabilization of the products but also in their formation.…”

Section: Resultsmentioning

confidence: 99%

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The Effect of Cluster Size on the Intra-Cluster Ionic Polymerization Process

Molina

Stein

2021

Molecules

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Polyaromatic hydrocarbons (PAHs) are widespread in the interstellar medium (ISM). The abundance and relevance of PAHs call for a clear understanding of their formation mechanisms, which, to date, have not been completely deciphered. Of particular interest is the formation of benzene, the basic building block of PAHs. It has been shown that the ionization of neutral clusters can lead to an intra-cluster ionic polymerization process that results in molecular growth. Ab-initio molecular dynamics (AIMD) studies in clusters consisting of 3–6 units of acetylene modeling ionization events under ISM conditions have shown maximum aggregation of three acetylene molecules forming bonded C6H6+ species; the larger the number of acetylene molecules, the higher the production of C6H6+. These results lead to the question of whether clusters larger than those studied thus far promote aggregation beyond three acetylene units and whether larger clusters can result in higher C6H6+ production. In this study, we report results from AIMD simulations modeling the ionization of 10 and 20 acetylene clusters. The simulations show aggregation of up to four acetylene units producing bonded C8H8+. Interestingly, C8H8+ bicyclic species were identified, setting a precedent for their astrochemical identification. Comparable reactivity rates were shown with 10 and 20 acetylene clusters.

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Section: Introductionsupporting

confidence: 76%

Section: Resultsmentioning

confidence: 99%

The Effect of Cluster Size on the Intra-Cluster Ionic Polymerization Process

Molina

Stein

2021

Molecules

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“…While the possibility of molecular formation upon ionization of van der Waals clusters (intracluster growth mechanism) has been demonstrated before (26,40,44), this paper forms a direct connection of such a mechanism with astronomical measurements. By applying the intracluster growth to acetylene and cyanoacetylene mixed clusters, we were able to successfully predict benzonitrile radical cation formation which was recently identified experimentally in TMC-1.…”

mentioning

confidence: 63%

“…Recently, using ab initio molecular dynamics (AIMD) to model ionization of small neutral acetylene clusters, the potential of this conversion mechanism for forming aromatic molecules has been demonstrated (26,40,44). This process can lead to molecular growth, whereby structures are formed on the C4 and C6 potential energy surfaces, among them the benzene cation (40).…”

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confidence: 99%

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Molecular dynamics reveals formation path of benzonitrile and other molecules in conditions relevant to the interstellar medium

Jose

Zamir

Stein

2021

Proc. Natl. Acad. Sci. U.S.A.

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Polycyclic aromatic hydrocarbons and polycyclic aromatic nitrogen heterocycles are believed to be widespread in different areas of the interstellar medium. However, the astronomical detection of specific aromatic molecules is extremely challenging. As a result, only a few aromatic molecules have been identified, and very little is known about how they are formed in different areas of the interstellar medium. Recently, McGuire et al. [Science 359, 202–205 (2018)] detected the simple aromatic molecule benzonitrile in Taurus Molecular Cloud-1. Although benzonitrile has been observed, the molecular mechanism for its formation is still unknown. In this study, we use quantum chemistry and ab initio molecular dynamics to model ionization processes of van der Waals clusters containing cyanoacetylene and acetylene molecules. We demonstrate computationally that the clusters' ionization leads to molecular formation. For pure cyanoacetylene clusters, we observe bond formation among two and three monomer units, whereas in mixed clusters, bond formation can also occur in up to four units. We show that the large amount of energy available to the system after ionization can lead to barrier crossing and the formation of complex molecules. Our study reveals the rich chemistry that is observed upon ionization of the clusters, with a wide variety of molecules being formed. Benzonitrile is among the observed molecules, and we study the potential energy path for its formation. These results also offer insights that can guide astronomers in their search for aromatic molecules in the interstellar medium.

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