Open (C2v) and closed (D3h) forms of the S3 molecule,thiozone

Ab initio molecular electronic structure theory has been used to predict the structures and relative energies of the normal and ring isomers of triatomic sulfur. Self-consistent-field theory was used in conjunction with a double zeta basis set S(11s7p/6s4p), augmented by three sets of s and p bond functions. After correction for the effects of electron correlation, the open and closed isomers of S₃ are predicted to be nearly comparable energetically, the open form lying lower by 4.3 kcal.