Dissociative electron attachment to sulfur dioxide : A theoretical approach

Abstract

In this present investigation, density functional theory (DFT) and natural bond orbital (NBO) calculations have been performed to understand experimental observations of dissociative electron attachment (DEA) to SO 2 . The molecular structure, fundamental vibrational frequencies with their corresponding intensities and molecular electrostatic potential (MEP) map, signifying the electron density contours, of SO 2 and SO − 2 are interpreted from respective ground state optimized electronic structures calculated using DFT. The MEPs are then quantified and the second order perturbation energies for different oxygen lone pair (n) to σ * and π * interactions of S-O bond orbitals have been calculated by carrying out NBO analysis and the results are investigated. 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 results of the calculations are used to interpret the dissociative electron attachment process. The dissociation of the anion SO − 2 into negative and neutral fragments has been explained by interpreting the infrared (IR) spectrum and the different vibration modes. It could be observed that the dissociation of the anion SO − 2 into S − occurs as a result of simultaneous symmetric stretching and bending modes of the molecular anion. While the formation of O − and SO − occurs as a result of anti-symmetric stretching of the molecular anion. The calculated symmetries of the TNI state contributing to the first resonant peak at around 5.2 eV and second resonant peak at around 7.5 eV could be observed from time-dependent density functional theory (TD-DFT) calculations to be an A 1 and a combination of A 1 +B 2 states for the two resonant peaks, respectively. These findings strongly support our recent experimental observations for DEA to SO 2 using the sophisticated velocity map imaging (VMI) technique [Jana and Nandi,

Study of S− and SO− ion formation from dissociative electron attachment to SO2

“…SO 2 is a tri-atomic molecule with C v 2 symmetry for both the neutral ground and negative ion states [26]. The C v 2 point group is characterized by the identity element, two mirror planes and one rotation axis.…”