Absorption Spectrum of Gaseous F- and Electron Affinities of the Halogen Atoms

Abstract

The absorption spectrum of gaseous fluoride ion has been observed in shock-heated vapors of CsF, RbF, and KF. The spectrum is a continuum with two sharp thresholds at 3595 and 3542 Å, similar to those of the other halide ions. The electron affinity determined from the low-energy threshold is 3.448±0.005 eV. The cross-section for photodetachment at 3565 Å is about 2.5±2×10−18 cm2 and at 3525, about 3.3±2×10−18 cm2. The electron affinities of chlorine, bromine and iodine are revised, respectively, to 3.613, 3.363, and 3.063 eV, all with uncertainties of 0.003 eV.