Radiative Capture of Electrons by Chlorine, Bromine, and Iodine Atoms

Absolute intensities were measured in the continuous emission spectrum resulting from electron attachment to the halogen atoms in a shock-heated plasma seeded with sodium halides. The intensity measurements were used to determine new photodetachment cross sections for the negative chlorine, bromine, and iodine ions in the wavelength region between 3000 and 4000 Å. These cross sections are presented here and, where possible, are compared with theoretical and experimental values obtained by other methods. For the case in which the halogen atom is left in the ground state (${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$), the present experiments give photodetachment cross sections of 1.2 × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ for ${\mathrm{Cl}}^{-}$, 2.0 × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ for ${\mathrm{Br}}^{-}$, and 2.2 × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ for ${\mathrm{I}}^{-}$ near the detachment thresholds.