2px-ray absorption of free transition-metal cations across the 3dtransition elements: Calcium through copper

Abstract

Experimental 2$p$ x-ray-absorption spectra of 3$d$ transition-metal cations in their electronic ground states were obtained in photoion-yield detection. Individual transitions are assigned within the $Z+1$ approximation and Hartree-Fock calculations, which reproduce the experimental spectra with good agreement. For 3$d$ transition metals, 2$p$ x-ray-absorption spectra are nearly identical for atoms and cations with equal 3$d$ electron configurations. The oscillator strengths of $2p\ensuremath{\rightarrow}3d$ transitions in 3$d$ transition-metal cations are proportional to the number of unoccupied 3$d$ states in accordance with bulk data. The ``continuum step'' does not coincide with the direct 2$p$ photoionization threshold but is related to resonant transitions into Rydberg states. For nickel cations, a 2$p$ core-hole lifetime of $1.6\ifmmode\pm\else\textpm\fi{}0.1$ fs is derived from the natural linewidth, which is $0.1$--$0.2$ eV smaller than for nickel adatoms and bulk because of the absence of inhomogeneous broadening.