Kinetic study of the reaction of vanadium and vanadium–titanium oxide cluster anions with SO2

Abstract

The reactivity of mass-selected V₄O₁₀⁻ cluster anions towards sulphur dioxide is investigated in an ion trap under multi-collision conditions. Gas phase reaction kinetics are studied as a function of temperature (T_R = 150–275 K). The binding energy of SO₂ to V₄O₁₀⁻ is obtained by analyzing the experimental low pressure rate constants, employing the Lindemann energy transfer model for association reactions in conjunction with statistical RRKM theory. In addition, infrared multiple photon dissociation spectroscopy is used in conjunction with density functional theory for the structural assignment of the [V₄O₁₀⁻, SO₂] complex, revealing a square pyramidal structure with the SO₂ molecule incorporated in the vanadium oxide framework. Energy profiles are calculated for the reaction between V₄O₁₀⁻ and V₆O₁₅⁻ with SO₂. Whereas the transition structures along the reaction pathway of V₄O₁₀⁻ with SO₂ have energies below those of the separated partners, the reaction of V₆O₁₅⁻ with SO₂ proceeds via a transition structure with energy higher than the educts. The role of cluster size and composition is investigated by studying the reaction kinetics of larger (V₆O₁₅⁻ and V₈O₂₀⁻) and titanium doped (V₃TiO₁₀⁻ and V₂Ti₂O₁₀⁻) vanadium oxide clusters with SO₂. The observed cluster size and composition dependencies are discussed.