[en] In this present investigation, the structures of SO₂, SO₂⁻, CO₂ and CO₂⁻ as well as the adiabatic electron affinities of the corresponding SO₂ and CO₂ neutral parents are computed using the infinite-order coupled-cluster method with all singles and doubles and non-iterative inclusion of triple excitations (CCSD(T)) and the Møller–Plesset perturbation theory up to the second order (MP2). The molecular structure, fundamental frequencies with their corresponding intensities and electron localization functions of SO₂ and SO₂⁻ are interpreted from respective ground-state optimized electronic structures calculated and compared with other simple tri-atomic molecules CO₂ and CO₂⁻, respectively. The electron localization function are then quantified and the second-order perturbation energies for different oxygen lone pairs (n) to σ^* and π^* interactions of S–O and C–O bond orbitals have been calculated by carrying out NBO analysis and the results are compared. The change in the electronic structure of the molecule after the attachment of a low-energy (≤15 eV) electron, thus forming a transient negative ion (TNI), can be interpreted from the n → σ^* and n → π^* interactions. The potential energy curves of SO₂–SO₂⁻ and CO₂– CO₂⁻ pairs are calculated as a function of S–O and C–O bond distance and bending angle. The adiabatic electron affinity of SO₂ is calculated to be positive while that of CO₂ is negative. Graphical abstract:

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