### 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 |
---|---|

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 |

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### ASJC Scopus subject areas

- Physical and Theoretical Chemistry

### Cite this

*Journal of Physical Chemistry A*,

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

**Equilibrium Geometry of the Ethynyl (CCH) Radical.** / Szalay, P.; Thøgersen, Lea S.; Olsen, Jeppe; Kállay, M.; Gauss, Jürgen.

Research output: Contribution to journal › Article

*Journal of Physical Chemistry A*, vol. 108, no. 15, pp. 3030-3034. https://doi.org/10.1021/jp036885t

}

TY - JOUR

T1 - Equilibrium Geometry of the Ethynyl (CCH) Radical

AU - Szalay, P.

AU - Thøgersen, Lea S.

AU - Olsen, Jeppe

AU - Kállay, M.

AU - Gauss, Jürgen

PY - 2004/4/15

Y1 - 2004/4/15

N2 - 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 rCC 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 rCC 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 rs and r0 geometries are shown not to be representative for the true equilibrium structure of CCH.

AB - 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 rCC 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 rCC 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 rs and r0 geometries are shown not to be representative for the true equilibrium structure of CCH.

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U2 - 10.1021/jp036885t

DO - 10.1021/jp036885t

M3 - Article

VL - 108

SP - 3030

EP - 3034

JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

SN - 1089-5639

IS - 15

ER -