The Electron Affinity Of Phosphorus

We have measured the energies of all three fine structure components in the P-3(J) ground state of the negative ion of phosphorus using laser photodetachment threshold spectroscopy. The experiment yielded an electron affinity of 746.68( 6) meV. The Delta J = 2-0, 2-1 and 1-0 fine structure splittings were determined to be 32.73( 7) meV, 22.48( 7) meV and 10.25( 3) meV, respectively. In the experiment, a mass selected beam of P- ions was merged with the output from a pulsed infrared optical parametric oscillator. The residual atoms produced in the photodetachment process were detected and used as a monitor of the photon- energy dependence of the relative cross section. The Wigner law was fitted to each of the three observed onsets of production of neutrals in order to extract the threshold energies.