Shallow electron centers in AgCl and AgBr have been studied by pulsed electron nuclear double resonance at 95 GHz. Information about the geometric structure and the ground-state wave function is obtained, which confirms that these centers consist of an electron loosely bound to a Coulombic trap. The microscopic models for these Coulombic traps, to which we are led, differ from the ones suggested from previous optical studies. It appears that the optical transition energies can be reasonably well accounted for by simple hydrogenlike and quantum-defect methods. Owing to the similarity between shallowly trapped and conduction electrons, information about the lowest state of the conduction band is derived, which reveals that this state is not mainly silver s like, as is frequently assumed, but also includes a substantial amount of chlorine s character. © 1996 The American Physical Society.

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