Electronic states and spectroscopic parameters of the iodocarbyne cation, CI+

Highlights: • First reliable characterization of potential energy curves of CI cation. • Characterization of the low-lying electronic states of CI. • Transition moments, transition probabilities, and radiative lifetimes. • Simulated single ionization spectrum of CI. We present a theoretical characterization of the cation iodocarbyne, CI⁺, using a correlated theoretical approach (SA-CASSCF/MRCI) to describe a manifold of singlet, triplet, and quintet electronic states. Reliable potential energy curves were constructed for both $\Lambda$+S and relativistic $\Omega$ states. Spin–orbit couplings strongly affect the energetic profile of the $\Lambda$+S representation. Spectroscopic parameters were calculated, and effects of core-valence correlation investigated. The transition dipole moment functions for the 1₁ ³${\Pi }_{0^{+}}$ $\to$ X₁ ¹${\Sigma }_{0^{+}}^{+}$ and 1₃ ³${\Pi }_1$ $\to$ X₁ ¹${\Sigma }_{0^{+}}^{+}$ states were evaluated and the corresponding radiative lifetimes obtained. Comparisons with other halocarbynes can now help understanding trends in properties in this class of molecules.