Article ID Journal Published Year Pages File Type
4440219 Atmospheric Environment 2011 10 Pages PDF
Abstract

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.

Research highlights► Formation of HOSO2 has been investigated using various quantum chemical methods. ► MP2 based methods predict a true structural transition state. ► QCISD energy corrections predict a barrier height close to experimental value. ► The reaction OH+SO2 ˗ HOSO2 is not barrierless.

Related Topics
Physical Sciences and Engineering Earth and Planetary Sciences Atmospheric Science
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