Ab initio configuration interaction studies of the electronic states of S2N2

Ab initio SCF and CI calculations are reported for the sulfur nitride, SN, and disulfur dinitride, S2N2, molecules. Calculations on SN, varying the internuclear distance, are performed using a variety of basis sets to determine a suitable basis for S2N2. The total energy, internuclear distance, and force constant of SN are reported for several choices of basis. Extended basis computations on S2N2 are performed, and midbond polarization functions are found to contribute significantly to a description of the ground state, affecting the higher MO's and the charge density. A prominent feature of the virtual spectrum is the existence of a low energy π* orbital which could play a role in low lying excited states, the polymerization process, and polymer conductivity. CI studies of the ground and excited states of S2N2 show several low lying singlet and triplet states of the type π→sigma*, π→π*, and sigma→π*, and possible identifications with experiment are discussed. A possibility of relating the observed paramagnetism on polymerization to (SN)/sub x/ to properties of the monomer S2N2 was considered, but the calculations do not support this hypothesis for the monomer in its square equilibrium geometry since no excited states were found to be accessible by thermal excitation