A quantum chemical calculation of the potential energy surface in the formation of HOSO2 from OH + SO2

Sanyasi Sitha, Linda L. Jewell, Stuart J. Piketh, Gerhard Fourie

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


The formation of HOSO2 from OH and SO2 has been thoroughly investigated using several different methods (MP2=Full, MP2=FC, B3LYP, HF and composite G* methods) and basis sets (6-31G(d,p), 6-31++G(d,p), 6-31++G(2d,2p), 6-31++G(2df,2p) and aug-cc-pVnZ). We have found two different possible transition state structures, one of which is a true transition state since it has a higher energy than the reactants and products (MP2=Full, MP2=FC and HF), while the other is not a true transition state since it has an energy which lies between that of the reactants and products (B3LYP and B3LYP based methods). The transition state structure (from MP2) has a twist angle of the OH fragment relative to the SO bond of the SO2 fragment of -50.0°, whereas this angle is 26.7° in the product molecule. Examination of the displacement vectors confirms that this is a true transition state structure. The MP2=Full method with a larger basis set (MP2=Full/6-31++G(2df,2p)) predicts the enthalpy of reaction to be -112.8 kJ mol-1 which is close to the experimental value of -113.3 ± 6 kJ mol-1, and predicts a rather high barrier of 20.0 kJ mol-1. When the TS structure obtained by the MP2 method is used as the input for calculating the energetics using the QCISD/6-31++G(2df,2p) method, a barrier of 4.1 kJ mol-1 is obtained (ZPE corrected). The rate constant calculated from this barrier is 1.3 × 10-13 cm3 molecule-1 s-1. We conclude that while the MP2 methods correctly predict the TS from a structural point of view, higher level energy corrections are needed for estimation of exact barrier height.

Original languageEnglish
Pages (from-to)745-754
Number of pages10
JournalAtmospheric Environment
Issue number3
Publication statusPublished - Jan 2011
Externally publishedYes


  • Atmospheric HSO formation
  • HOSO
  • Quantum chemical calculations
  • SO

ASJC Scopus subject areas

  • General Environmental Science
  • Atmospheric Science


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