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

作者：Sitha Sanyasi^*; Jewell Linda L; Piketh Stuart J; Fourie Gerhard

来源：Atmospheric Environment, 2011, 45(3): 745-754.

DOI：10.1016/j.atmosenv.2010.09.018

• Atmospheric H2SO4 formation
• Quantum chemical calculations
• HOSO2
• SO2

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 degrees, whereas this angle is 26.7 degrees 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(2df2p) method, a barrier of 4.1 kJ mol(-1) is obtained (ZPE corrected). The rate constant calculated from this barrier is 1.3 x 10(-13) cm(3) 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.

• 出版日期2011-1