Electric-quadrupole transition-rate measurement of a highly charged ion in an electron-beam ion trap using pulsed laser excitation from a metastable state

We present the lifetime measurement of the ${\left(4d_{3/2}^{-1}5s\right)}_{J=2}$ state in Pd-like ${\mathrm{I}}^{7+}$, which predominantly decays to the $(4d^{10}{)}_{J=0}$ ground state by an electric-quadrupole transition modified by strong spin-orbit mixing. We measure this microsecond-order lifetime in an electron-beam ion trap using pulsed laser excitation from a metastable state which is continuously populated by electron collisions. The measured lifetime provides a new benchmark for relativistic atomic structure calculations with $d$-state electrons.

Figure 1

Energy levels in Pd-like ${\mathrm{I}}^{7+}$ calculated with fac [44]. The transition of interest, ${(4d^{10})}_{J=0}$–($4d_{3/2}^{-1}{5s)}_{J=2}$, and the cascade processes contributing to the repopulation of ($4d_{3/2}^{-1}{5s)}_{J=2}$ are also shown.

Figure 2

Experimental scheme with the energy diagram of ${\mathrm{I}}^{7+}$.

Figure 3

Bottom: Experimentally observed LIF decay profile. The red line represents the fitting result. Top: Residuals of the experimental plots from the fitting line. Error bars reflect Poisson counting statistics.

Figure 4

Active space set dependence of the E2 transition line strength (in atomic units) in the MCDF calculation without the RCI correction. The thin black lines represent the experimental uncertainty ($1\sigma$).