Binding energies and structure of transition metal negative ions

Abstract

The photoelectron spectra of 11 transition metal negative ions have been obtained in a crossed beam experiment using a sputter type ion source and a fixed frequency ArII laser (488 nm). The electron affinities (E.A.’s) are measured to be E.A.(Ti)=0.080±0.014 eV, E.A.(V)=0.526±0.012 eV, E.A.(Cr)=0.667±0.010 eV, E.A.(Zr)=0.427±0.014 eV, E.A.(Nb) =0.894±0.025 eV, E.A.(Mo)=0.747±0.010 eV, E.A.(Rh)=1.138±0.008 eV, E.A.(Pd)=0.558±0.008 eV, E.A.(Ta)=0.323±0.012 eV, E.A.(W)=0.816±0.008 eV, and E.A.(Ir)=1.566±0.008 eV. The ground states of the negative ions of these elements are determined from analysis of the photoelectron spectra and all are found to be of a dks2 configuration with the exception of Pd−(d10 s). Excited electronic states of Pd−[(4d95s2) 2D5/2] and Ta−[(5d46s2) 3P0] are identified. Calculation of relative intensities of photelectron transitions is used extensively in the analysis of the spectra and is compared with experiment for a number of cases. The spin–orbit separations for Rh−(3F) and Ta−(5D) are measured and compared with values obtained from ratio isoelectronic extrapolation. The accuracy of this extrapolation technique is discussed and an extensive table of extrapolated splittings for transition metal negative ions is given. Plots of the s-electron binding energies of the transition metal negative ions versus the number of d electrons exhibit smooth trends and striking similarities for each of the three transition series.