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Long Carbon-Based Chains of Interstellar Medium Can Have a Triplet Ground State. Why Is This Important for Astrochemistry?

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journal contribution
posted on 09.04.2019 by Ioan Bâldea
The identification of linear carbon chain molecules in the interstellar medium (ISM) requires the correct assignment of their most stable isomers. Recent theoretical work on linear carbons done in the astrophysics/astronomy community claimed that out of the classes of linear carbon chains astronomically observed, all carbon-based chains with an even number of electrons possess singlet ground electronic states. Contrary to this view, we report here detailed DFT and CCSD­(T) theoretical results demonstrating that the most stable isomer of the linear HC10N molecule is a triplet. Our study suggests that with a proper assignment of the electronic ground state, HC10N can still be identified in astronomical data, similar to the adjacent members HC9N and HC11N of the homologous HCnN series, which have long been reported in extraterrestrial media. The results presented in this paper are useful both for astrochemistry and for the general chemical science. The presently reported CCSD­(T)-based values of the ionization and electron attachment energies can help further astrochemical modeling of the ISM. From a more general perspective, the results of this paper are interesting also because they provide important insight into the relationship between bond lengths and bond orders. We show that this relationship can be quantitatively described by means a simple analytic formula, which represents a modification of that proposed empirically by Pauling.