Ab initio study on the molecular structure and spectroscopic properties of isomers of SO₃

The exploration for the four possible isomers of sulfur trioxide (SO₃) has led to the analysis of spectroscopic constants and anharmonic force fields for cis-OSOO, trans-OSOO, OS(=O) O and SOOO. Quantum chemical calculations are performed with Density Functional Theory (DFT) by employing B3LYP, B3P86 and B3PW91 three different functionals, in combination with Dunning's correlation-consistent cc-pVnZ, aug-cc-pVnZ (n = T, Q) basis sets. The equilibrium geometries, energies, force constants, a series of spectroscopic constants of these four isomers of SO₃ are calculated. The relationship between their structures and spectroscopic properties are analyzed in detail. The present results well reproduce the previous corresponding theoretical or experimental values. Therefore, we hope that our predictions on the isomers of SO₃ can provide the useful reference to further study their spectroscopic properties.