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

Venkatesan S. Thimmakondu, Amir Karton

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20 Citations (Web of Science)


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] hepta1,5-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 (mu not equal 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.

Original languageEnglish
Pages (from-to)17685-17697
Number of pages13
JournalPhysical Chemistry Chemical Physics
Issue number27
Publication statusPublished - 21 Jul 2017


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