Vibrational Properties of the Disulfur Dinitride Molecule, S2N2: IR and Raman Spectra of the Matrix-Isolated Molecule

The IR and Raman spectra of disulfur dinitride, S2N2, are reported not only for the solid condensate but also for the molecules isolated in solid noble gas, N-2, or CH4 matrices at low temperatures. The results imply that the isolated S2N2 molecule has much the same geometry as in the crystalline solid with a virtually square-planar structure conforming to D-2h, symmetry, a conclusion confirmed by isotopic enrichment in N-15 and by the results of earlier as well as fresh quantum chemical calculations. These calculations also support the results of normal coordinate analysis of the experimental data in giving potential constants suggestive of a relatively rigid S2N2 molecule consistent with its description as a 2 pi-electron aromatic, while appearing to maintain a formal S-N bond order close to 1.