Stepwise ionization of Mo$^{14+}$ ions in EBIT: The importance of the metastable level

TL;DR

This study investigates the ionization process of Mo$^{14+}$ ions in an EBIT, emphasizing the role of metastable states, through experimental measurements and theoretical calculations of energy levels, transitions, and ionization cross sections.

Contribution

It provides a detailed analysis of stepwise ionization involving metastable levels, combining experimental data with theoretical modeling to explain ionization mechanisms of Mo$^{14+}$ ions.

Findings

Metastable level 3p$^{6}$3d$^{9}$4s plays a crucial role in ionization.

Theoretical calculations agree with experimental measurements.

Stepwise ionization explains the presence of Mo$^{15+}$ ions at low electron energies.

Abstract

The visible spectrum of Mo$^{15+}$ ions was measured using a high-temperature superconducting electron-beam ion trap at the Shanghai EBIT Laboratory, with an electron beam energy $E_{e}$=400 eV, significantly lower than the ionization potential (IP=544.0 eV) of Mo$^{14+}$ ions in the ground state. To expound on the experiment, the energy level structure, radiative transition properties, electron-impact excitation, and electron-impact ionization cross section for both the ground state and low-lying excited state of the Mo$^{14+}$ ions were calculated using Dirac-Fock-Slater method with a local central potential and distorted wave approximation. The results demonstrated reasonable agreement with both available experimental and theoretical data. Through an analysis of the related atomic processes of Mo$^{14+}$ ion, a scenario involving the stepwise ionization of the metastable state 3p$^{6}$3d$^{9}$4s was proposed to explain the presence of the Mo$^{15+}$ ions with a lower energy of the incident electron. Finally, the significance of the metastable levels in ionizing Mo$^{14+}$ ions is highlighted.