Theoretical investigation of excited dipole bound states of alkali-containing diatomic anions

Information about electronic excited states of molecular anions plays an important role in investigating electron attachment and detachment processes. Here we present a high-level theoretical study of the electronic structures of 12 alkali-metal-containing diatomic anions MX⁻ (MX = LiH, LiF, LiCl, NaF, NaCl, NaBr, RbCl, KCl, KBr, RbI, KI and CsI). The equation-of-motion electron-attachment coupled-cluster singles and doubles (EOM-EA-CCSD) method is used to calculate the electron binding energies (EBEs) of 10 electronic excited states of each of the 12 molecule anions. With addition of different s-/p-/d-type diffusion functions in the basis set, we have identified possible excited dipole bound states (DBSs) of each anion. With the investigation of EBEs on the 12 MXs with dipole moment (DM) up to 12.1 D, we evaluate the dependence of the number of anionic excited DBSs on molecular DM. The results indicate that there are at least two or three DBSs of anions with a molecular DM larger than 7 D and a molecule with DM > 10 D can sustain a π-DBS of the anion. Our study has some implications for the excited DBS electronic states of alkali-metal-containing diatomic molecules.