Electron paramagnetic resonance spectra of singly charged surface oxygen vacancies ($F$ or color centers) formed by electron bombardment on a single-crystalline MgO film under UHV conditions are reported. The embedding of the defect in a well-defined geometrical environment allows not only for the determination of the magnetic quantities but also, in conjunction with STM studies, for the geometrical assignment of the observed signal to color centers located on the edges of the MgO film.

• Received 11 February 2005

DOI:https://doi.org/10.1103/PhysRevLett.94.186101