Abstract
Sulfur dioxide was photochemically oxidized to SO₃⁻ on the surface of magnesium oxide in the presence of adsorbed water vaopor and oxygen or nitrous oxide. Water reacted with adsorbed SO₂ to increase the concentration of sulfite ions and monodentate sulfito complexes. Subsequent photolysis led to the formation of S0₃⁻, which was confirmed by the EPR hyperfine structure of the ion enriched with sulfur-33. Molecular oxygen or nitrous oxide serve as electron scavengers, thus increasing the surface concentration of SO₃⁻. The greater stability of SO₃⁻ on the surface relative to aqueous solutions is attributed to the lack of mobility in the adsorbed water. The half-life of the surface SO₃⁻ was >10 hr at 25°C, but decreased to 0.5 min at 100°C. Surface sulfite ions were completely transformed to sulfate ions and sulfato complexes upon heating at 600°C in an ambient atmosphere. The reaction of H₂O and SO₂ at 25°C produced H₂O, elemental sulfur, and sulfite ions on the surface of MgO. Furthermore, a paramagnetic ion attributed to S₂O⁻ was formed when H₂S and SO₂ were allowed to react on MgO at 25°C. The EPR spectrum of S₂O⁻ is characterized by two sets of hyperfine lines with a (subscript xx)(1) = 48.6 G and a(subscript xx)(2 ) = 32.6 G. The other principal values of the hyperfine tensor were less than one gauss. No hyperfine structure was detected when ¹⁷O was introduced via sulfur dioxide. The principal g values are g(subscript xx) = 2.001, g(subscript yy) = 2.030 and g(subscript zz) = 2,010, The concentration of the surface species S₂O⁻ was enhanced by irradiation at 254 or at 366 nm. The S₂O⁻ was also formed by irradiation of adsorbed COS or CS₂. A proposed mechanism for the formation of S₂O⁻ involves the reaction of elemental sulfur as S₂ with oxide ions of the MgO surface..
Lin, Mei-Jan (1976). Structure and reactivity of sulfur-containing molecules adsorbed on magnesium oxide. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -508681.