Excited dipole bound electronic states of potassium iodide anions: A theoretical perspective

The information about electronic excited states of molecular anions is of pivotal importance for understanding electron attachment/detachment processes. Here, we present a high-level theoretical study on electronic states of potassium iodide anions (KI−). By the evaluation of different basis sets, we present accurate spectroscopic constants of the anionic ground electronic state using the multireference configuration interaction with Davidson correction method. The equation-of-motion electron-attachment coupled-cluster singles and doubles method is carried out to calculate electron binding energies (EBEs) of electronic states. With the addition of different s-/p-/d-diffusion functions in the basis set, we have identified possible excited dipole bound states (DBSs) of KI−. The results indicate that, owing to the large dipole moment of KI molecules, the anions can hold three excited DBSs, i.e., two σ-type DBSs and one π-type DBS, with the EBEs of 39 meV (σ-DBS1), 4.7 meV (π-DBS), and only 1.8 meV (σ-DBS2) below the neutral ground state. Molecular orbitals, potential energy curves, and spectroscopic constants of DBSs are presented. Our study would shed some light on the electronic states of potassium iodide molecular anions.