Understanding the binding in excited states of the yttrium anion

Recent experimental studies, for example those by Rui Zhang et al. [J. Chem. Phys., 2023, 158, 084303], have provided a precise new value for the electron affinity of the yttrium atom and fresh insights into its excited states. However, a comprehensive theoretical understanding of its binding and electron affinity remains lacking. Inspired by these findings, we present a detailed theoretical investigation of the excited-state electronic structure of Y^-. To achieve this, we employ the multiconfiguration Dirac-Hartree-Fock (MCDHF) method, as well as the relativistic infinite-order two-component (IOTC) approach combined with multiconfiguration complete active space self-consistent field (CASSCF) and second-order multireference perturbation theory (CASPT2). Spin-orbit coupling effects are incorporated using the restricted active space state interaction (RASSI) method with atomic mean field integrals (AMFI). Our IOTC CASSCF/CASPT2 calculations yield an electron affinity (EA) of 0.298 eV in spin-free computations and 0.258 eV when spin-orbit effects are included via RASSI, representing one of the most accurate theoretical predictions to date. Notably, our results closely align with the recent experimental measurement of 0.3113 eV, reinforcing the reliability of our approach and deepening our understanding of the electronic structure and binding in Y^-. Our investigation highlights potential discrepancies between the predicted symmetries of the excited states of the yttrium anion and experimental observations. Additionally, we calculated the binding energies for transitions from Y^- to Y and identified four potential bound or quasi-bound states in the yttrium anion.