Lifetime determination of the $\mathrm{Fe}\mathrm{XIV}$ $3s^{2}3p{}^{2}P_{3∕2}^o$ metastable level

The lifetime of the $3s^{2}3p{}^{2}P_{3∕2}^o$ first excited energy level of $\mathrm{Fe}\mathrm{XIV}$ (Al like) was measured at the Heidelberg electron beam ion trap by monitoring its optical decay to the ground state by a magnetic dipole $\left(M1\right)$ forbidden transition at $\lambda =530.29\mathrm{nm}$ (green coronal line), a well-known line in stellar spectra. A new trapping scheme has been applied. Possible systematic effects were investigated by studying the dependence of the decay curves on various trapping conditions with high statistical significance. The result of ${16.726}_{-0.010}^{+0.020}\mathrm{ms}$ shows an unexplained discrepancy in the average value of existing theoretical predictions. The inclusion of the electron anomalous magnetic moment within the theoretical calculations increases this disagreement, thus pointing at other possible origins of this discrepancy.

Figure 1

(Color online) Schematic drawing of the experimental setup.

Figure 2

(Color online) Photon counts vs the electron beam accelerating voltage. The acquisition time for each data point of the various curves was $10\mathrm{s}$. For these measurements the electron beam was kept constantly on (no switching).

Figure 3

(Color online) Typical single-lifetime fluorescence decay curve (logarithmic scale) and its residual (bottom). The electron beam was turned off for $1\mathrm{s}$ at a measurement cycle of $2\mathrm{s}$. For this measurement, data were accumulated for about $18\mathrm{h}$. The inset shows the same data after background subtraction of 1337 counts per channel (10-fold binning).

Figure 4

(Color online) Measured lifetimes as a function of the drift tube trapping potential. The dashed line serves only to guide the eye. The total acquisition time for all data points was about $160\mathrm{h}$.

Figure 5

(Color online) Loading and trapping scheme for the lifetime measurement. Shown is one single measurement cycle of $2\mathrm{s}$.

Figure 6

(Color online) Weighted average of data points recorded at trapping potentials between $500\mathrm{V}$ and $1800\mathrm{V}$ (solid line). The black lines represent the $1\sigma$ standard deviation.

Figure 7

Part of the level scheme of $\mathrm{Fe}\mathrm{XIV}$. Shown is the fine-structure splitting of the ground-state configuration with the metastable ${}^{2}P_{3∕2}^o$ level. The metastable $3s3p3d{}^{4}F_{9∕2}^o$ state features only $M1$ and $M2$ transistions (branching ratio 40–60%) and has a caluclated lifetime of about $19\mathrm{ms}$. Due to low excitation cross section compared to the ${}^{2}P_{3∕2}^o$ level, repopulation of the level of interest can be taken as negligible (see text).

Figure 8

(Color online) Theoretical and experimental lifetimes. The numbers on the $x$ axis label the results obtained by different theoretical treatments and experimental methods. Corresponding references can be found in Table . Solid circles are theoretical predictions as they were published; triangles represent the calculated values corrected for the EAMM. Experimental results are indicated by open circles. The inset compares the here reported experimental value with the measurement from the LL-EBIT. The two upwards pointing arrows indicate theoretical values that are outside the plotting range of the figure ($19.8\mathrm{ms}$ for label 7 and $21.38\mathrm{ms}$ for label 11).