High-resolution determination of the electron affinity of fluorine and bromine using crossed ion and laser beams

We report tunable-laser photodetachment of F- and Br- ions near the first threshold corresponding to the atomic P3/22 ground state. Using a high-resolution pulsed uv laser calibrated with molecular iodine absorption and doubly crossed laser and ion beam technique, we determine the electron affinities of fluorine and bromine with high accuracy. These determinations account for the hyperfine structure of the atomic ground states of F19 and Br79,81Br. The threshold values obtained for the transition between the ion ground state S01 and the atomic ground hyperfine state P3/22 are 27 432.440(25) cm-1 or 3.401 190(4) eV for fluorine and 27 129.170(15) cm-1 or 3.363 590(3) eV for bromine, and the isotope shift of Br-, Br79 is found to be below our experimental resolution.