Electron affinity of gallium and fine structure of Ga-: Experiment and theory

Binding energies of fine structure levels of the negative ion of gallium have been determined both experimentally and theoretically, resolving long-standing discrepancies for the electron affinity of gallium. The relative photodetachment cross section from Ga-(4p2P0,1,23) was measured using tunable laser spectroscopy over the photon energy range 270-400 meV (4600-3100 nm). Observed photodetachment thresholds were used to measure the electron affinity of Ga to be 301.20(11) meV and the fine structure splittings of Ga-to be 23.31(19) meV for J=0-1 and 62.4(5) meV for J=0-2. The binding energies of the negative ion states were independently calculated using the multireference extrapolated intermediate Hamiltonian relativistic Fock space coupled cluster method in large, converged four-component Gaussian-spinor basis sets. The Dirac-Fock-Breit Hamiltonian was used, and leading quantum electrodynamic effects were added. All calculations were carried out in spherical symmetry, correlating all electrons and fully including core effects. The calculated electron affinity is 302(3) meV, and the fine structure splittings are 22(2) meV for J=0-1 and 60(2) meV for J=0-2, which are all in excellent agreement with the present measurements. These results substantially improve both the accuracy and precision of the Ga electron affinity and provide a determination of the fine structure of Ga-.