MEASUREMENT OF THE RADIATIVE DECAY RATE AND ENERGY OF THE METASTABLE (2s2p1/253s1/2)(J=0) LEVEL IN Fe XVII

Measurements at the Livermore electron beam ion trap have been performed in order to infer the energy and the radiative lifetime of the (1s(2)2s(2)2p(1/2)(5)3s(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 angstrom, feeding the population of the (1s(2)2s(2)2p(3/2)(5)3s(1/2))(J=1) upper level of one of the most prominent lines in the Fe XVII L-shell X-ray spectrum, commonly dubbed 3G. In the presence of a strong (>= few kG) magnetic field, the (1s(2)2s(2)2p(1/2)(5)3s(1/2))(J=0) level has a finite probability to decay directly to the (1s(2)2s(2)2p(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 (1s(2)2s(2)2p(1/2)(5)3s(1/2))(J=0) level to the (1s(2)2s(2)2p(3/2)(5)3s(1/2))(J=1). Our result of (1.45 +/- 0.15) x 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 angstrom, which means that the line is displaced 1.20 +/- 0.05 eV from the neighboring (2s(2)2p(1/2)(5)3s(1/2))(J=1) -> (2s(2)2p(6))(J=0) transition, commonly labeled 3F. From our measurement, we infer 5950570 +/- 710 cm(-1) for the energy of the (1s(2)2s(2)2p(1/2)(5)3s(1/2))(J=0) level.