STRUCTURES, ENERGIES AND VIBRATIONAL-SPECTRA OF 4 ISOMERS OF HYDROGENDIOXOTHIOSULFATE(IV) ANION (HS2O2-) AND OF THE RELATED ANION CLSO2- - AN AB-INITIO MOLECULAR-ORBITAL STUDY

The ground-state geometries. energies, atomic charges and vibrational wavenumbers of four isomeric forms of the HS2O2- anion as well as of the related ClSO2- anion have been calculated at the HF/6-311G(**) and HF/6-311++G(**) levels. Electron correlation has been taken into account according to second order Moller-Plesset perturbation theory (MP2). The most stable isomer of HS2O2- is HSSO2- 1 the formation of which from SO2 and HS- is exothermic by ca. 108 kJ mol(-1) (calculated reaction energy). The analogous formation of ClSO2- from SO2 and Cl- is exothermic by 79 kJ mol(-1). Slightly less stable than 1 are HOS(SO- 2 and HS(S)O-2(-) 4 and least stable is the isomer HOSSO3(-) Anions 1-3 are of C-1 symmetry and 4 as well as ClSO2- are of C-s symmetry. The likely intermediates of the reaction between H2S and SO2 in its early stage are discussed. The calculated wavenumbers of the fundamental modes of ClSO2- agree well with experimental data.