Ab initio study of the cyclic isomers of N2S4

An ab initio study of the three possible isomers of cyclic N2S4 is reported. Calculations of minima and transition states at the SCF and MP2 levels of theory are presented, using a DZP basis set with and without model potentials on the sulfur atom. The lowest energy structure for the 1,3-isomer is an asymmetric chair structure, consistent with experimental studies. For the 1,4-isomer, an asymmetric chair is the minimum at the SCF level and there are two minima at the MP2 level; a symmetric chair and a twisted-planar structure. The 1,2-isomer was the most stable structure at the SCF level, having two minimum conformations; a twisted-chair and a symmetrical boat, however these could not be confirmed at the MP2 level. The two experimental IR bands which have been attributed to the 1,4-isomer are compared with the harmonic bands from our MP2 calculations for the 1,4-chair singlet isomer of N2S4.