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Generation and structural characterization of Ge carbides GeCn (n = 4, 5, 6 ) and GeC5 by laser ablation, broadband rotational spectroscopy, and quantum chemistry

Abstract

Following the recent discovery of T-shaped \ce{GeC2}, rotational spectra of three larger Ge carbides, linear \ce{GeC4}, \ce{GeC5}, and \ce{GeC6} have been observed using chirped pulse and cavity Fourier transform microwave spectroscopy and a laser ablation molecule source, guided by new high-level quantum chemical calculations of their molecular structure. Like their isovalent Si-bearing counterparts, Ge carbides with an even number of carbon atoms beyond \ce{GeC2} are predicted to possess $^1\Sigma$ ground electronic states, while odd-numbered carbon chains are generally $^3\Sigma$; all are predicted to be highly polar. For the three new molecules detected in this work, rotational lines of four of the five naturally occurring Ge isotopic variants have been observed between 6 and 22\,GHz. From these measurements, the \ce{Ge-C} bond lengths have been determined to high precision: the derived values of 1.776\,\AA~for \ce{GeC4}, 1.818\,\AA~for \ce{GeC5}, and 1.782\,\AA~ for \ce{GeC6} indicate a double bond between these two atoms. Somewhat surprisingly, the spectrum of \ce{GeC5} very closely resembles that of a $^1\Sigma$ molecule, implying a spin-spin coupling constant $\lambda$ in excess of 770\,GHz for this radical, a likely consequence of the large spin-orbit constant of atomic Ge ($\sim$1000\,cm$^{-1}$). A systematic comparison between the production of SiC$_n$ and GeC$_n$ chains by laser ablation has also been been undertaken. The present work suggests that other large metal-bearing molecules may be amenable to detection by similar means.

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Publication details

The article was received on 26 Jun 2019, accepted on 11 Aug 2019 and first published on 13 Aug 2019


Article type: Paper
DOI: 10.1039/C9CP03607E
Phys. Chem. Chem. Phys., 2019, Accepted Manuscript

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    Generation and structural characterization of Ge carbides GeCn (n = 4, 5, 6 ) and GeC5 by laser ablation, broadband rotational spectroscopy, and quantum chemistry

    K. Lee, S. Thorwirth, M. Martin-Drumel and M. C. McCarthy, Phys. Chem. Chem. Phys., 2019, Accepted Manuscript , DOI: 10.1039/C9CP03607E

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