Thermochemistry of the association reaction and enthalpy of formation of : A quantum chemical study

The thermochemistry of the HOSO 4 radical is of crucial importance for the modeling of the atmospheric sulfur-oxidation cycle, in which HOSO 4 is formed in the reaction HOSO 2 + O 2 + M → HOSO 4 + M (2a). We performed high-level quantum chemical calculations to characterize the energetics of reaction (2a) and obtained the following values for the enthalpy of reaction: Δ R H 0 K (2a) = −71.4 ± 2.0 and Δ R H 298 K (2a) = −72.9 ± 3.0 kJ/mol. For the enthalpy of formation of HOSO 4 , it follows: Δ f H 0 K ( HOSO 4 ) = - 438.0 ± 5.0 kJ / mol and Δ f H 298 K ( HOSO 4 ) = - 447.0 ± 6.0 kJ / mol . These new thermochemical data can serve as a basis for kinetic studies of HOSO 4 reactions in the atmosphere.