### Abstract

The equilibrium geometry of the ethynyl (CCH) radical has been obtained using the results of high-level quantum chemical calculations and the available experimental data. In a purely quantum chemical approach, the best theoretical estimates (1.208 Å for r_{CC} and 1.061-1.063 Å for r _{CH}) have been obtained from CCSD(T), CCSDT, MR-AQCC, and full CI calculations with basis sets up to core-polarized pentuple-zeta quality. In a mixed theoretical-experimental approach, empirical equilibrium geometrical parameters (1.207 Å for r_{CC} and 1.069 Å for r _{CH}) have been obtained from a least-squares fit to the experimental rotational constants of four isotopomers of CCH which have been corrected for vibrational effects using computed vibration-interaction constants. These geometrical parameters lead to a consistent picture with remaining discrepancies between theory and experiment of 0.001 Å for the CC and 0.006-0.008 Å for the CH distances, respectively. The corresponding r_{s} and r_{0} geometries are shown not to be representative for the true equilibrium structure of CCH.

Original language | English |
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Pages (from-to) | 3030-3034 |

Number of pages | 5 |

Journal | Journal of Physical Chemistry A |

Volume | 108 |

Issue number | 15 |

DOIs | |

Publication status | Published - Apr 15 2004 |

### ASJC Scopus subject areas

- Physical and Theoretical Chemistry

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## Cite this

*Journal of Physical Chemistry A*,

*108*(15), 3030-3034. https://doi.org/10.1021/jp036885t