MEASUREMENT OF THE RADIATIVE DECAY RATE AND ENERGY OF THE METASTABLE LEVEL IN Fe xvii

Abstract

ABSTRACT Measurements at the Livermore electron beam ion trap have been performed in order to infer the energy and the radiative lifetime of the ( 1 s 2 2 s 2 2 p 1 / 2 5 3 s 1 / 2 ) J = 0 ?> level in the Fe xvii spectrum. This is the longest-lived level in the neonlike iron ion, and its radiative decay produces the Fe xvii line at 1153 Å, feeding the population of the ( 1 s 2 2 s 2 2 p 3 / 2 5 3 s 1 / 2 ) J = 1 ?> upper level of one of the most prominent lines in the Fe xvii L-shell X-ray spectrum, commonly dubbed 3 G ?> . In the presence of a strong ( ≥ ?> few kG) magnetic field, the ( 1 s 2 2 s 2 2 p 1 / 2 5 3 s 1 / 2 ) J = 0 ?> level has a finite probability to decay directly to the ( 1 s 2 2 s 2 2 p 6 ) J = 0 ?> neonlike ground level via the emission of an L-shell X-ray. Our measurements allow us to observe this X-ray line in the Fe xvii L-shell spectrum and from it to infer the radiative rate for the magnetic dipole decay of the ( 1 s 2 2 s 2 2 p 1 / 2 5 3 s 1 / 2 ) J = 0 ?> level to the ( 1 s 2 2 s 2 2 p 3 / 2 5 3 s 1 / 2 ) J = 1 ?> . Our result of ( 1.45 ± 0.15 ) × 10 4 ?> s−1 is in agreement with predictions. We have also measured the wavelength of the associated X-ray line to be 16.804 ± 0.002 Å, which means that the line is displaced 1.20 ± 0.05 eV from the neighboring ( 2 s 2 2 p 1 / 2 5 3 s 1 / 2 ) J = 1 → ( 2 s 2 2 p 6 ) J = 0 ?> transition, commonly labeled 3 F ?> . From our measurement, we infer 5950570 ± 710 cm−1 for the energy of the ( 1 s 2 2 s 2 2 p 1 / 2 5 3 s 1 / 2 ) J = 0 ?> level.