A nonplanar cyclic minimum-energy structure of singlet C<sub>9</sub>

Slanina, Zdenêk; Sl, Lee; François, J; Kurtz, Joe; Adamowicz, Ludwik; Smigel, Murray D.

doi:10.1080/00268979400101021

Cited by 10 publications

(2 citation statements)

References 43 publications

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“…Slanina and co-workers 76 have suggested that the ground state structure of C 8 is nonplanar, since they find a boat-shaped structure with D 2 d symmetry as the global minimum at the MP2/6-31G* level. However, this level of theory produces a number of artifactual results: as seen in Table , it incorrectly predicts cyclic C 6 to have D 6 h symmetry, and it also (for example, see ref ) yields a nonplanar global minimum for cyclic C 9 with manifestly unphysical harmonic frequencies. There are thus grounds for scepticism about MP2/6-31G* predictions for C 8 .…”

Section: Resultsmentioning

confidence: 99%

Structure and Vibrations of Small Carbon Clusters from Coupled-Cluster Calculations

1996

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The vibrational spectrum of the linear carbon clusters C2−C9 and of cyclic C4, C6, C8, and C10 has been investigated using the augmented coupled-cluster, CCSD(T), method and correlation-consistent basis sets. Particular emphasis is placed on assignment of bands in matrix infrared spectra of trapped graphite vapor. The relative energetics of linear and cyclic isomers of C6, C8, and C10 were investigated at the CCSD(T) level using basis sets of [4s3p2d1f] quality. Our best calculations predict that the ground state structure of C6 is a cumulenic D 3h ring and that of C8 a polyacetylenic C 4h ring. Linear states are close in energy (13 ± 2 and 8 ± 2 kcal/mol, respectively), and both forms should be observable. The ground state structure of cyclic C10 clearly has D 5h rather than D 10h symmetry, at least for the r e geometry. A linear regression of computed CCSD(T)/[3s2p1d] harmonic frequencies vs observed fundamentals for the previously assigned stretching frequencies of linear C n clusters has a very high correlation coefficient (up to r = 0.99975 at 10 data points). From the regression line and the calculated frequencies, band origins for linear C8 are predicted at 2063 ± 18 and 1711 ± 14 cm-1 (99% confidence intervals) and ancillary bands for linear C9 at 2093 ± 18 and 1604 ± 16 cm-1. From the calculated infrared-active CCSD(T) frequencies for the cyclic clusters and anharmonicity considerations, we suggest that bands near 1695, 1818, and 1915 or 1921 cm-1 belong to cyclic C6, C8, and C10, respectively, while bands near 1590 and 1715 cm-1 are probably due to linear C9 and C8, respectively. Finally, a broad feature at 2070−2090 cm-1, which upon deconvolution appears to consist of three bands, is suggested to contain bands of both linear C8 and C9.

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Section: Resultsmentioning

confidence: 99%

Structure and Vibrations of Small Carbon Clusters from Coupled-Cluster Calculations

1996

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“…They obtained a C s nonplanar structure, lying just 6 kcal/mol above the linear ground state, at the MP2/6-31G* level. 266 However, more recent calculations by Martin et al showed the cyclic structure to be a planar monocyclic ring of C 2v symmetry, for which the relative energy was 9 kcal/ mol above the chain. 58 Once again, the MP2 results were shown to be artifactual.…”

Section: A Theorymentioning

confidence: 99%