Lifetimes of some O II levels by beam-foil experiments

Abstract

Using the beam-foil technique and rather low beam energies (in the range 216-296 keV) in order to reduce cascade corrections, we have determined lifetimes for the , and terms of O II and compared them with predictions from various theoretical and experimental approaches. Our results support the claim for a short average lifetime. Experimental lifetimes for , and have been determined for the first time. The first two compare well with the opacity project results, whereas the experimental lifetime of level, a pseudo-five-electron system lying above the O II ionization limit, is a factor of four smaller.

Theoretical lifetimes for certain O II levels

“…C for Coulomb, B for length gauge result. Numbers in parenthesis denote powers of 10 GRASP 6.07 (7) 5.46 (7) 5.42 (7) 5.42(7) 3s' 2 D 5/2 8.31 (7) 9.93(7) 9.45 (7) (7) 3.03 (7) 4.50 (7) 4.74(7) 3p 4 P o 5/2 9.14(7) 1.06 (8) 5.67(7) (8) vious theoretical numbers as well as a recent measurement [30]. Difficulties inherent in early beam-foil measurements are reflected on the differences exhibited between independent theoretical predictions and certain experimental values [37].…”

“…The 3s was obtained by freezing the rest of the orbitals and performing an AL calculation on all odd relativistic configurations generated from the non-relativistic configurations 2p 3 , 2p 2 3p and 2s 1 2p 3 3s. Finally, the 3d was obtained by freezing the rest of the orbitals and performing an AL calculation on all odd relativistic configurations generated from the non-relativistic [20] Beam-foil, curve fitting b [21] Beam-foil, curve fitting c [22] Beam-foil, curve fitting d [23] Ion beam with a gas target, curve fitting e [24] Beam-foil f [25] Beam-foil, curve fitting g [26] Beam-foil h [27] Beam gas method, curve fitting i [28] Beam-foil, cascade effects suppressed experimentally j [29] Beam-foil j1 [29] Beam-foil, corrected for cascading k [30] Beam-foil, curve fitting l [31] Beam-foil, ANDC analysis l1 [31] Beam-foil, curve fitting m [32] Beam-foil, ANDC analysis n [33] Beam-foil, curve fitting configurations 2p 3 , 2p 2 3p , 2s 1 2p 3 3s and 2s 1 2p 3 3d. Freezing of orbitals at each step of this procedure has been adopted, since the AL calculations were performed on levels differing widely in energies.…”

“…In Table 2 we report lifetimes for the fine structure levels of the 3d 4 P and 4 D terms, which were found to be J-dependent in the current theoretical investigation. We now focus on the 3p 4 D o and 3p 2 D o level lifetimes, for which the disparity between theoretical and certain experimental results has already been noted in [11] and has been the object of a recent experimental investigation [30]. In the calculation for the 3p 4 D o J=7/2 level lifetime, 378 CSFs have been considered for the level of interest and a total of 607 CSFs for all the even J=5/2 lower lying O II levels that may link to it through electric dipole transitions.…”

Oscillator strengths and transition probabilities of O II

“…Lifetimes of all 707 excited fine structure levels of O II are available electronically, and a sample of lifetimes is given in [17](b), [9](c), [10](d), [18](e), [4](f). NTr represents the number of radiative decays of the level.…”

“…Quite a number of studies have been carried out for radiative transitions and lifetimes of O II, both theoretically, for example, by Lennon and Burke [4] as part of the Opacity Project [5], Bell et al [6] whose values were renormalized for a number of transitions by Wiese et al [7], Natarajan [8], Bates and Damgaard [9], Froese Fischer [10], and experimentally, for example, by Edlen [11], Eriksson [12], Pattersson and Wenaker [13], Veres and Wiese [14], del Val et al [15], Coetzer et al [16], and Nandi et al [17]. An evaluated compilation of O II transitions from earlier investigations was carried out by Wiese et al [7].…”