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Issue 27, 2017
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Energetic and spectroscopic properties of the low-lying C7H2 isomers: a high-level ab initio perspective

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Abstract

We use high-level ab initio CCSD(T) and CCSDT(Q) methods to investigate the energetic and spectroscopic properties of nine low-lying isomers of C7H2, which lie within 1 eV. Among these, heptatriynylidene (1), 1-(buta-1,3-diynyl)cyclopropenylidene (2) and heptahexaenylidene (9) have been detected experimentally. The other six isomers, 1,2-(diethynyl)cyclopropenylidene (3), bicyclo[4.1.0]hepta-1,2,4,5-tetraene-7-ylidene (4), cyclohepta-1,2,3,4-tetraen-6-yne (5), bicyclo[4.1.0]hepta-4,6-diene-2-yne-7-ylidene (6), bicyclo[4.1.0]hepta-1,5-diene-3-yne-7-ylidene (7) and 1-(buta-1,3-diynyl)propadienylidene (8), remain hypothetical to date. Except for 1, all of the isomers are associated with a non-zero dipole moment (μ ≠ 0). Although Fourier-transform microwave spectroscopy had detected 2 and 9, our study reveals that six hypothetical isomers (3–8) are thermodynamically sandwiched between the experimentally known and astronomically relevant isomers 2 and 9. The structural parameters, dipole moments, rotational and centrifugal distortion constants, harmonic vibrational frequencies, and infra-red intensities presented here may be useful for the laboratory detection of these previously unidentified isomers (3–8) and also all others (2–9) in astronomical sources.

Graphical abstract: Energetic and spectroscopic properties of the low-lying C7H2 isomers: a high-level ab initio perspective

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Article information


Submitted
01 May 2017
Accepted
22 Jun 2017
First published
23 Jun 2017

This article is Open Access

Phys. Chem. Chem. Phys., 2017,19, 17685-17697
Article type
Paper

Energetic and spectroscopic properties of the low-lying C7H2 isomers: a high-level ab initio perspective

V. S. Thimmakondu and A. Karton, Phys. Chem. Chem. Phys., 2017, 19, 17685
DOI: 10.1039/C7CP02848B

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