Quantum chemical study on the equilibrium geometries of S3 and S−3, The electron affinity of S3 and the low lying electronic states of S−3

Abstract

The geometries and relative stabilities of the open, C2v symmetric and closed, D3h symmetric forms of thiozone and its anion, the adiabatic electron affinity of S3 and the energies of the three low-lying excited electronic states of the thiozone anion (Ã 2B2,B̃ 2A1,C̃ 2A2) at the optimized geometry of the X̃ 2B1 ground state are computed employing coupled-cluster [CCSD(T)], second-order multireference perturbation theory (CASPT2), and multireference CI (MRCI and IC-MRCI) methods using large atomic natural orbital basis sets. In addition, the saddle point for the open→closed isomerization on the neutral S3 potential energy surface is being studied. Surprisingly, the calculations do not show the expected underestimation of the experimentally determined electron affinity, in sharp contrast to test calculations on the sulfur atom, the disulfur molecule, and earlier results for ozone. Apart from this, thiozone and its anion behave in many respects qualitatively similar as ozone and O−3, while quantitatively various differences are observed.