Accurate electron affinity of Ga and fine structures of its anions

We report the high-resolution photoelectron spectra of negative gallium anions obtained via the slow-electron velocity-map imaging method. The electron affinity of Ga is determined to be 2429.07(12) cm^-1 or 0.301 166(14) eV. The fine structures of Ga are well resolved: 187.31(22) cm^-1 or 23.223(27) meV for ³P₁ and 502.70(28) cm^-1 or 62.327(35) meV for ³P₂ above the ground state ³P₀, respectively. The photoelectron angular distribution for photodetachment from Ga^-(4s²4p^{2 3}P₀) to Ga(4s²5s ²S_1/2) is measured. An unexpected perpendicular distribution instead of an isotropic distribution is observed, which is due to a resonance near 3.3780 eV.