The cross sections for photodetachment of the alkali halide negative ions NaClminus;, NaBrminus;, and NaIminus;have been measured in the photon energy range 2.0ndash;2.3 eV. In this energy range, well above the photodetachment threshold at approximately 0.6 eV, the only processes energetically accessible are photodetachment to produce the ground electronic state neutral alkali halide, and photodissociation. For each of the sodium halides, we observe a single isolated resonance in the cross section, occurring approximately 160 cmminus;1to the high energy side of the neutral sodium atom 3sndash;3penergy difference. This resonance is interpreted as autodetachment of a2Pgr; state of the negative ion imbedded in the photodetachment continuum. TheXthinsp;2Sgr;ndash;Athinsp;2Pgr; energy difference in NaXminus;is almost completely halide independent, providing strong support for the qualitative picture of the negative ion as being composed of a neutral sodium atom adjacent to a closed shell halide ion. Qualitative fits of the experimental data utilizing the Fano formalism indicate that the lifetime of the autodetaching state is on the order of 10minus;12sec and that the shape of the potential well for the2Pgr; state is virtually identical to that of the negative ion ground state.
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