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Molecular Growth upon Ionization of Van Der Waals Clusters Containing HCCH and HCN is a Pathway to Prebiotic Molecules

preprint
submitted on 22.06.2020, 10:49 and posted on 24.06.2020, 10:09 by Tamar Stein, Partha P. Bera, Timothy J. Lee, Martin Head-Gordon
The growth mechanisms of organic molecules in an ionizing environment such as the interstellar medium are not completely understood. Here we examine by means of ab initio molecular dynamics (AIMD) simulations and density functional theory (DFT) computations the possibility of bond formation and molecular growth upon ionization of Van der Waals clusters of pure HCN clusters, and mixed clusters of HCN and HCCH, both of which are widespread in the interstellar medium. Ionization of van der Waals clusters can potentially lead to growth in low temperature and low-density environments. Our results show, that upon ionization of the pure HCN clusters, strongly bound stable structures are formed that contain NH bonds, and growth beyond pairwise HCN molecules is seen only in a small percentage of cases. In contrast, mixed clusters, where HCCH is preferentially ionized over HCN, can grow up to 3 or 4 units long with new carbon-carbon and carbon-nitrogen covalent bonds. Moreover, cyclic molecules formed, such as the radical cation of pyridine, which is a prebiotic molecule. The results presented here are significant as they provide a feasible pathway for molecular growth of small organic molecules containing both carbon and nitrogen in cold and relatively denser environments such as in dense molecular clouds but closer to the photo-dissociation regions, and protoplanetary disks. In the mechanism we propose, first, a neutral van der Waals cluster is formed. Once the cluster is formed it can undergo photoionization which leads to chemical reactivity without any reaction barrier.

History

Email Address of Submitting Author

tamar.stein@mail.huji.ac.il

Institution

The Hebrew University of Jerusalem

Country

Israel

ORCID For Submitting Author

0000-0003-3155-2273

Declaration of Conflict of Interest

Statement on conflicts of interest: MHG is a part-owner of Q-Chem Inc.

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