FTIR and computational studies of pure and water containing SO3 species in solid argon matrices

The FT infrared spectrum in the 4000–400 cm−1 range of SO3 vapors, matrix isolated in argon and in water doped argon solid layers, is reported. Vibrational bands are assigned to pure SO3 monomeric and polymeric species and to SO3⋯H2O complexes, on the basis of theoretical B3LYP and MP2 calculations employing the aug-cc-pVTZ basis sets. The spectroscopic evidence suggests that in addition to the monomer, both the dimeric and the cyclic trimeric (SO3)n complexes are the only other SO3 forms present in the matrix. The spectra also indicate the presence of the 1:1 and the 1:2 SO3·H2O complexes as well as traces of H2S2O7 and water complexed H2SO4, but no evidence for a stable 2:1 SO3⋯H2O complex was found. The occurrence of the various species is discussed in the light of their calculated energies.