Observation of electric octupole emission lines strongly enhanced by the anomalous behavior of a cascading contribution

Abstract

We present extreme ultraviolet spectra of Ag-like W 27+ observed with an electron beam ion trap. In the spectra, the 4f 7/2,5/2 -5s transitions are identified as the first observation of spontaneous electric octupole emission. Our theoretical investigation shows that the emission line intensity is strongly and specifically enhanced at the atomic number 74 by an anomalous behavior of cascading contribution to 5s via 5p ← 5d.

High resolution X-ray spectra of the time evolution of emission from metastable electronic states of highly charged Ni-like ions

“…Since these states can have sufficiently long lifetimes, further electron impacts can ionize them to higher charge states, a process often referred to as ladder ionization. It has been found significant in few-electron charge states outside of a closed electronic shell, for example Pd-like ions [2][3][4][5], Ag-like ions [6,7], and Ni-like ions [8][9][10][11][12]. It is particularly important in non-Maxwellian, quasimonoenergetic plasmas with electron energies below the ionization threshold as higher charge states would not be present without this ionization from an excited state.…”