### Abstract

An ab initio multiconfiguration Hartree-Fock (MCHF) study of the X̃ ^{1}Σ_{g}
^{+}, a ̃^{3}Σ, _{u}
^{+} B̃ ^{1}Δ_{u}, and C̃ ^{1}Π_{u} states of cyanogen (C_{2}N_{2}) is presented. Equilibrium structures, harmonic vibrational frequencies, excitation energies, and dissociation energies have been calculated and found to be in semiquantitative agreement with available experimental data. This study confirms the π→π* character of C_{2}N_{2} (ã ^{3}Σ_{u}
^{+}) and C_{2}N_{2} (B̃ ^{1}Δ_{u}), and the n→;π* character of C_{2}N_{2} (C̃ ^{1}Π_{u}) near their equilibrium structures. Configuration mixing among the n and π electrons is needed to correct the broken symmetry description given by the Hartree-Fock (HF) method, and leads to a qualitatively correct representation of these states. For C_{2}N_{2} (ã ^{3}Σ_{u} ^{+}) and C_{2}N_{2} (B̃ ^{1}Δ _{u}), the harmonic force constants show a strong through-bond interaction which is due to the dominance of the charge transfer configuration ^{+}NCCN^{-}. For C_{2}N_{2} (C̃^{1}Π_{u}) the trans-bending vibrational mode and the cis-bending mode lead to different Renner-Teller splittings: the lower ^{1}A′ state most likely has a slightly trans-bent minimum energy structure. The calculated harmonic stretching frequencies of C_{2}N _{2} (C̃ ^{1}Π_{u}) are v_{1} (sym. CN str.)=2145 cm^{-1}, v_{2} (CC str.)=989 cm^{-1}, and v_{3} (asym. CN str.)=1789 cm^{-1}.

Original language | English |
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Pages (from-to) | 265-272 |

Number of pages | 8 |

Journal | Journal of Chemical Physics |

Volume | 83 |

Issue number | 1 |

Publication status | Published - 1985 |

### ASJC Scopus subject areas

- Atomic and Molecular Physics, and Optics

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## Cite this

*Journal of Chemical Physics*,

*83*(1), 265-272.