Electron affinities of B, Al, Bi, and Pb

A sputter ion source has been used to obtain beams of B−, Al−, Bi−, and Pb− ions. A mass analyzed beam of each of these ions was crossed with a fixed frequency argon ion laser operating at 488 nm, and a photoelectron spectrum obtained at a resolution of 60 meV. From an analysis of these data the following electron affinities were obtained: B, 0.278±0.010 eV; Al, 0.442±0.010 eV; Bi, 0.947±0.010 eV; Pb, 0.365±0.008 eV. In addition, a1D excited state of Al− was observed 0.332±0.010 eV above the ground state of the negative ion.