A kinetic study of the reactions of vanadium, iron, and cobalt with sulfur dioxide

Abstract

A kinetic study of the reactions of ground state V, Fe, and Co with SO₂ is reported. V, Fe, and Co were produced by the 248 nm photodissociation of VCl₄, ferrocene, and Co(C₅H₅)(CO)₂, respectively, and were detected by laser-induced fluorescence. V + SO₂ proceeds by an abstraction reaction with rate constants given by k = (2.33 ± 0.57) × 10⁻¹⁰ exp[−(1.14 ± 0.19) kcal mol⁻¹/RT] cm³ molecule⁻¹ s⁻¹ over the temperature range 296–571 K. Fe + SO₂ was studied in the N₂ buffer range of 10–185 Torr between 294 and 498 K. The limiting, low-pressure third-order rate constants are given by k₀ = (3.45 ± 1.19) × 10⁻³⁰ exp[−(2.81 ± 0.24) kcal mol⁻¹/RT] cm⁶ molecule⁻² s⁻¹. Co + SO₂ was studied in the CO₂ buffer range of 5–40 Torr between 294 and 498 K. This reaction is independent of temperature over the indicated range and has a third-order rate constant of k₀ = (5.23 ± 0.28) × 10⁻³¹ cm⁶ molecule⁻² s⁻¹. Results of this work are compared to previous work on the Sc, Ti, Cr, Mn, and Ni + SO₂ systems. The reaction efficiencies for the abstraction reactions depend on the ionization energies of the transition metal atoms and on the reaction exothermicities, and the reaction efficiencies of the association reactions are strongly dependent on the energies needed to promote an electron from a 4s² configuration to a 4s¹ configuration.