# Advancing Our Understanding of the Excited States of the Tantalum Anion

## TL;DR

This paper calculates the energy levels and electron affinity of tantalum and its ions using advanced theoretical methods, revealing new insights into the tantalum anion's excited states.

## Contribution

The study provides the most accurate theoretical electron affinity for tantalum and identifies discrepancies in the symmetry of its anion's excited states.

## Key findings

- The electron affinity of tantalum was calculated as 0.321 eV, closely matching the experimental value of 0.329 eV.
- Four potential bound or quasi-bound states were identified in the tantalum anion.
- Discrepancies were found between the predicted symmetry of excited states and experimental observations.

## Abstract

Our study provides
a comprehensive theoretical examination of the
energy levels associated with the neutral tantalum atom and its ions
in various charge states (Ta, Ta+, and Ta–), employing the multiconfiguration Dirac–Hartree–Fock
(MCDHF) method, and relativistic infinite order two-component (IOTC)
method with multiconfiguration complete active space self-consistent
field (CASSCF) followed by the second-order single-state multireference
perturbation (CASPT2) methods. The effect of spin–orbit (SO)
coupling is introduced via the restricted active space state interaction
(RASSI) method, utilizing atomic mean field SO integrals (AMFI). Through
IOTC CASSCF/CASPT2 RASSI calculations, we determined the electron
affinity (EA) of the tantalum atom to be 0.321 eV, which stands among
the most accurate theoretical values achieved to date. This result
closely aligns with the experimental measurement of 0.329 eV. Our
investigation highlights potential discrepancies between the predicted
symmetry of the excited states of the tantalum anion and experimental
observations. Additionally, we calculated the bonding energies for
transitions from Ta– to Ta and identified four potential
bound or quasi-bound states in the tantalum anion.