Issue 27, 2017

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

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

Supplementary files

Article information

Article type
Paper
Submitted
01 May 2017
Accepted
22 Jun 2017
First published
23 Jun 2017
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2017,19, 17685-17697

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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