Experimental evidence for the hyperfine interaction between a surface superoxide species on MgO and a neighbouring hydroxylic proton

Abstract

The superoxide O^–₂ radical ion has been generated at the surface of MgO by two different methods both involving the parallel formation of surface hydroxyls. EPR spectra at 77 K reveal the presence of only one species with a hyperfine structure due to weak dipole–dipole interaction with a nearby hydroxyl (B_x= 0.37 mT, B_y= 0.21 mT, B_z= 0.10 mT). The set of B data is satisfactorily reproduced by a simple model for the dipolar interaction envisaging a T-shaped O^–₂⋯H species. Calculated geometrical features are in excellent agreement with a plausible structure for the superoxide species sitting on low-coordinate Mg²⁺ and interacting with the hydrogen of an adjacent hydroxyl.