Infrared spectra of SO₃ polymers and complexes in rare gas matrices

Infrared spectra of SO₃ 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 SO₃ Lewis base. Several SO₃·X complexes were prepared and identified in doubly doped neon matrices. The observations suggest that the SO₃·OH₂ complex does not rearrange to H₂SO₄ in the 5 K neon matrix.