A microwave and ab initio investigation of N2-SO3, OC-SO3, and OC-SO3-Ar

M. B. Craddock, C. S. Brauer, K. J. Higgins, K. R. Leopold

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Microwave spectra have been observed for N2-SO3, OC-SO3, Ar-SO3-CO, and several of their isotopic derivatives. All three complexes are symmetric tops with little or no out-of-plane distortion of the SO3. In Ar-SO3-CO, the Ar and CO lie on opposite sides of the sulfur, an arrangement which has not been previously observed for trimers involving SO3. In N 2-SO3 and OC-SO3, the N-S and C-S bond lengths are 2.934(12) and 2.854(12), respectively. In Ar-SO3-CO, the C-S distance is 2.849(4) Å, which is identical, within the estimated uncertainties, to that in OC-SO3. The Ar-S distance, on the other hand, is 3.411(11) Å, which represents a small but distinct lengthening of 0.061(12) Å relative to that previously determined for Ar-SO 3. Stark effect measurements for OC-SO3 and Ar-SO 3-CO give dipole moments of 0.8488(13) and 0.602(15) D, respectively. The latter is very nearly equal to the difference between the dipole moments of OC-SO3 and Ar-SO3, suggesting that the dipole moment of the trimer is simply the vector sum of the unperturbed dimer dipole moments. Counterpoise corrected optimized geometries and binding energies have been computed at the MP2/aug-cc-pVTZ level for Ar-SO3 (1.08 kcal/mol), N2-SO3 (2.60 kcal/mol), OC-SO3 (3.92kcal/mol), and Ar-SO3-CO (4.90 kcal/mol). The binding energy of Ar-SO 3-CO is nearly equal to the sum of the Ar-SO3 and OC-SO3 binding energies, indicating that the two-body interactions on opposite sides of the SO3 plane are not strongly coupled. Taken together, the experimental and theoretical results indicate that Ar-SO 3-CO is best regarded as a composite of Ar-SO3 and OC-SO3 moieties.

Original languageEnglish (US)
Pages (from-to)63-73
Number of pages11
JournalJournal of molecular spectroscopy
Issue number1
StatePublished - Nov 2003

Bibliographical note

Funding Information:
This work was supported by the National Science Foundation, the Donors of the Petroleum Research Fund, administered by the American Chemical Society, and the Minnesota Supercomputer Institute. We are also grateful to Professor William Klemperer for initially introducing one of us to the virtues of SO 3 , and for the many subsequent years of inspiration and support.


  • Ab initio
  • Complexes
  • Dipole moment
  • Intermolecular forces
  • Lewis acidity
  • Molecular structure
  • Sulfur trioxide


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