Dissociation, absorption and ionization of some important sulfur oxoanions (S2On2−n = 2, 3, 4, 6, 7 and 8)

• Theoretical study on the dissociation, absorption and ionization of S2On2− oxoanions.
• Calculating absorption spectra of the anions TD-DFT employing M062X functional.
• The effect of microhydration and electrostatic field of solvent on the absorption.
• Ionization energies of the anions were calculated using SAC–CI method.

In this work, a systematic theoretical study was performed on the dissociation, absorption and ionization of several important sulfur oxoanions (S2On2− (n = 2, 3, 4, 6, 7 and 8)). ΔEelec (thermal corrected energy), ΔH° and ΔG° of the dissociation reactions of the oxoanions to their radical monoanions were calculated using combined computational levels of theories such as Gaussian-3 (G3) and a new version of complete basis set method (CBS-4M) in different environments including gas phase, microhydrated in gas phase and different solvents. Calculations showed S2O72− is the most stable anion against the dissociation to its radical monoanions (SO4− + SO3−). It was also found that S2O42− has more tendency to dissociate to its radical anions (SO2− + SO2−) compared to the other anions. The absorption spectra of the anions were also calculated using the time-dependent density functional theory (TD-DFT) employing M062X functional. The effect of microhydration and electrostatic field of solvent on the different aspects (intensity, energy shift and assignment) of the absorption spectra of these anions were also discussed. It was observed that both hydrogen bonding and electrostatic effect of water increases the intensity of the absorption spectrum compared to the gas phase. Effect of microhydration in shifting the spectra to the shorter wavelength is considerably higher than the effect of electrostatic field of water. Finally, several gas phase ionization energies of the anions were calculated using the symmetry-adapted cluster–configuration interaction methodology (SAC–CI) and found that the first electron detachment energies of S2O22−, S2O32− and S2O42− are negative. Natural bonding orbital (NBO) calculations were also performed to assign the electron detachment bands of the anions.

Sulfur oxoanions dissociate to their radical anions in the gas phase.Figure optionsDownload as PowerPoint slide