Infrared spectra of SO 3 polymers and complexes in rare gas matrices

Infrared spectra of SO ₃ and of its polymers in rare gas matrices were examined. While the in-plane vibrational modes showed little gas-matrix and matrix to matrix shifts, the out-of-plane ν₂ vibration showed much larger medium sensitivity. This was attributed to formation of axial complexes with the more polarizable rare gases donating electrons to the SO ₃ Lewis base. Several SO ₃·X complexes were prepared and identified in doubly doped neon matrices. The observations suggest that the SO ₃·OH ₂ complex does not rearrange to H ₂SO ₄ in the 5 K neon matrix.