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Updated: Jun 28, 2026

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Theoretical studies on low-lying electronic states of cyanocarbene HCCN and its ionic states
Zeng-Xia Zhao1, Hong-Xing Zhang, Chia-Chung Sun
1Institute of Theoretical Chemistry, State Key Laboratory of Theoretical and Computational Chemistry, Jilin University, Changchun 130023, People's Republic of China.
Abstract:
Geometries of 10, 7, and 6 low-lying states of the HCCN neutral radical, its anion and cation, were optimized by using the complete active space self-consistent field (CASSCF) method in conjunction with the aug-cc-pVTZ basis set, respectively. Taking the further correlation effects into account, the second-order perturbations (CASPT2) were carried out for the energetic correction. Vertical excitation energies (T(v)) at the ground state geometry of the HCCN neutral radical were calculated for 11 states. The results of our calculations suggest that the spin-allowed transitions of HCCN at 4.179, 4.395, 4.579, 4.727 and 5.506 eV can be attributed to X(3)A'' --> 2(3)A'', X(3)A'' --> (3)A', X(3)A --> 3(3)A'', X(3)A'' --> 2(3)A', and X(3)A'' --> 3(3)A', respectively. The singlet-triplet splitting gap of HCCN is calculated to be 0.738 eV. The vertical and adiabatic ionization energies were obtained to compare with the PES data. The results we obtained were consistent with the available experiment results.
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