Laser spectroscopic measurements of binding energies and fine-structure splittings of Co-, Ni-, Rh-, and Pd-

A tunable infrared laser source is utilized to study the photodetachment threshold spectra of the transition-metal negative ions Co-, Ni-, Rh-, and Pd-. The binding energies of the respective ionic ground states are found to be 663.3(6), 1157.16(12), 1142.89(20), and 562.14(12) meV. In addition, a 3F4-3F3 fine-structure splitting of 875(15) cm-1 is measured for Co-, and the 2D5/2-2D3/2 splitting of Ni- is determined to be 1485(3) cm-1. For Pd-, the electronically excited 4d95s2 2D5/2 state is found to lie 1127(4) cm-1 above the 4d105s 2S1/2 ionic ground state, i.e., it is bound by 422.4(5) meV. The results agree with previous values obtained from laser photodetached electron spectra, but constitute improvements in accuracy of up to two orders of magnitude.