Measurements and modeling of electric-dipole-forbidden 2p{sub 1/2}-2p{sub 3/2} transitions in fluorinelike U{sup 81+} through berylliumlike U{sup 88+}
- Department of Physics and Space Technology, Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)
We report the observation of electric-dipole-forbidden 2p{sub 1/2}-2p{sub 3/2} transitions in berylliumlike, boronlike, carbonlike, nitrogenlike, oxygenlike, and fluorinelike uranium. Our measurement identified nine magnetic dipole transitions, as well as one strong electric quadrupole transition in carbonlike U{sup 86+} that has not been observed in lower-{ital Z} ions because of collisional quenching. The measurement was carried out with a high-resolution crystal spectrometer, and an accuracy as good as 35 ppm was obtained in the determination of the transition energies. The transitions are significantly less affected by quantum electrodynamical effects than analogous electric-dipole-allowed transitions in these ions. The data thus provide benchmarks for theoretical approaches of electron-electron correlation effects in the high-{ital Z} limit Z{alpha}{approx}1 that complement earlier measurements of 2s-2p transitions in such highly charged ions. The accuracy of the present measurements, however, was sufficient to determine the residual contributions from quantum electrodynamics (about 2 eV) with an accuracy of 5{percent}, i.e., with an accuracy comparable to that of the best measurements of such contributions to the 1s ground level in hydrogenic U{sup 91+}. The contributions from quantum electrodynamics are in large part due to the vacuum polarization terms. The 2p{sub 1/2}-2p{sub 3/2} transition energies thus provide a handle for testing the accuracy of vacuum polarization terms nearly independent of the terms arising from the electron self energy. Results from collisional-radiative calculations are presented that show that the forbidden lines are almost exclusively produced by indirect processes, i.e., radiative cascades, radiative electron capture, and the ionization of 2p{sub 1/2} electrons. This is in stark contrast to the electric dipole-allowed transitions, which are mostly populated by direct electron-impact excitation. {copyright} {ital 1998} {ital The American Physical Society}
- OSTI ID:
- 641631
- Journal Information:
- Physical Review A, Vol. 58, Issue 3; Other Information: PBD: Sep 1998
- Country of Publication:
- United States
- Language:
- English
Similar Records
Zeeman splitting and g factor of the 1s{sup 2}2s{sup 2}2p {sup 2}P{sub 3/2} and {sup 2}P{sub 1/2} levels in Ar{sup 13+}
Resonance enhancement of electron collision rates for fluorinelike ions