Ab initio MO study of the geometries and energetics of the C3H− anion

The molecular structures of various conformers of the C3H− anion were studied using complete active space SCF and QCISD(T) methods. A Huzinaga-Dunning split-valence (or double-zeta) plus polarization (D95v∗∗ or D95∗∗) basis set was used. The relative stability ladder of the computed stationary points and their relative positions on the potential energy surface are discussed using single- and multi-reference SDCI with the Davidson correction and CCSD(T); the general contraction scheme of the [5s3p2d1f/3s2p1d] atomic natural orbitals and the 6-311 + + G(2d, p) basis sets were applied, respectively. The global minimum of the C3H− anion is a C2v singlet (1A1) with a C3 ring, which is aromatically stabilized due to the 4n + 2 (n = 0) π electrons in the C3 ring. Below the theoretical electron detachment energy of the anion (2.3 eV), 1A1, several electronic states, 1Δ, 3A″, 1A″ and 1A′, with different symmetries are predicted.