Raman Spectral Studies of Oleums

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Abstract
Relative integrated Raman intensities of oleums reported earlier [G. E. Walrafen and T. F. Young, Trans. Faraday Soc. 56, 1419 (1960)] have been redetermined, and the measurements have been extended to other Raman bands. The new intensity data indicate low degrees of dissociation of H2S2O7, and they constitute evidence for the presence of small amounts of H2O3O10. When X(SO3), the stoichiometric mole fraction of a mixture of sulfur trioxide and sulfuric acid, is increased from zero to 0.3, relative integrated intensities of Raman bands of H2SO4 and of H2S2O7 are observed to decrease or to increase, respectively, in nearly perfect agreement with corresponding variations of Σ[H2SO4] and Σ[H2S2O7], the stoichiometric sulfuric or disulfuric acid molarities. These agreements indicate that [HS2O7—] is small, and they provide an explanation for the observed low electrical conductivities. When X(SO3) is increased above 0.3, however, SO3 and H2S3O10 appear and increase in concentration, while [H2S2O7] attains a maximum value of 9.8 mole·liter—1 at X(SO3)≈0.5, and [H2SO4] approaches zero at X(SO3)=0.6. Above X(SO3)=0.6, S3O9 makes its appearance and increases in concentration as [H2S3O10] attains a maximum value of ∼1.4 mole liter—1 at X(SO3)≈0.74. [SO3] and [S3O9] continue to increase until X(SO3)=1.0, at which composition [SO3]≈17.4 mole·liter—1 and [S3O9]≈2.1 mole·liter—1. Vibrational frequencies of S2O72—, HS2O7—, and H2S2O7 obtained from studies of molten K2S2O7 and (NO2++HS2O7—), and from studies of oleums, have been compared, and the vibrations have been assigned and correlated with the aid of polarization data. The intensity data obtained from studies of molten (NO2++HS2O7—) provide additional evidence that HS2O7— concentrations are generally low in oleum solutions. Vibrations of SO3, H2S3O10, and S3O9 are also considered briefly.

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