The paramagnetic ion H2S2 was formed by allowing H2S molecules at -78 °C to react with trapped electrons on MgO. Two forms of H2S2" (HSS'H'-) were identified by their EPR spectra. Species A is characterized bygj, = 2.015 and^| = 2.003 with ( ) = 9.4 G, aH'(A) = 6.6 G and a j_s(A) =* a±s'(A) =* -2G,a¡|s(A) = 61 G, 0|¡S'(A) = 41 G; whereas, species B is characterized by gi30(B) = 2.009 with oisoH(B) = 9.4 G, a¡soH'(B) = 6.6 G and aisos(B) = 13 G, aisos'(B) = 9 G. Species A was more stable and dominated the spectrum upon irradiation at -196 °C following the reaction of H2S with trapped electrons at the surface. Species B was highly mobile. The spin density of the unpaired electron was predominantly localized in the 3p orbitals of the two nonequivalent sulfur atoms of the H2S2~r adical.

Publication costs assisted by the Environmental Protection Agency SO2 is photochemically oxidized to SO3on the surface of magnesium oxide in the presence of adsorbed water vapor and oxygen or nitrous oxide. Water reacts with adsorbed SO2 to increase the concentration of sulfite ions and monodentate sulfito complexes. Subsequent photolysis leads to the formation of SO3-, which is confirmed by the EPR hyperfine structure of the ion enriched with sulfur-33. Molecular oxygen or N2O serve as electron scavengers, thus increasing the surface concentration of SO3-. The greater stability of S03on the surface relative to aqueous solutions is attributed to the lack of mobility in the adsorbed water. The half-life of the surface SO3-is >10 hr at 25°, but drops to 0.5 min at 100°.

Ruthenium ions in zeolite Y form complexes with CO and 02 which have well-resolved EPR spectra. Addition of CO at 298 K resulted in the formation of a Ru3+ monocarbonyl complex or a polycarbonyl complex, depending on the partial pressure of CO. The monocarbonyl complex was characterized by g± = 2.0600 and gy = 1.9871, whereas the polycarbonyl complex was characterized by g_L = 2.0593, g2 = 2.471, and g3 = 1.9970. Hyperfine coupling for 13C and the two ruthenium isotopes, "Ru and 101Ru, indicates that the unpaired electron is primarily localized (ca. 70%) on the metal ion. Upon reaction of the monocarbonyl complex with 02 at 298 K, the spectrum of a superoxide ion was observed. The Ru3+ appears to be oxidized to Ru4+, and the reversible nature of the spectrum indicates that CO and 02 are simultaneously coordinated to the ruthenium. The spectrum of the complex formed with 1702 suggests that the oxgyen nuclei are nonequivalent.

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