Beam-foil spectroscopy of oxygen in the wavelength region from 270 to 490 Å

Abstract

We have used the beam-foil technique to study the spectrum of oxygen between 270 and 490 Å. We have measured the mean lives of the 3d2F, 3d4P, 3d4D, 3d′ 2D, 3d′ 2F, 4d4P, and 4d4D terms of O II, the 3s1P0, 3s3P0, 3S5P, 3s′ 3D, 3d3P, 3d3D, 3d3F, and 3d5P terms of O III, and the 3S2S, 3P2P0, and 3s4P0 terms of O IV. All cascade components are adequately explained. Good agreement is found with previous measurements in most cases, but significant discrepancies are found with some earlier results obtained using branches above 2000 Å. Generally satisfactory agreement is also found with theoretical predictions, although disagreement is found for several members of the 2p3–2p23d array in O II f-Values are computed for 18 individual lines, and compared with other experimental and theoretical results. Finally, we discuss briefly the f-value trends along the 2p23P–2p3s3P0 (O III), 2p21D–2p3s1P0 (O III), 2s2p24P–2s2p(3P0)3s4P0 (O IV), and 2p2P0–3s2S (O IV) isoelectronic sequences.

Theoretical lifetimes for certain O II levels

“…We now proceed to discuss existing experimental results for the 3d 4 D level lifetime. Our theoretical average lifetime for the 3d 4 D term does not agree with the experimental results in [25,32], but is closer (Table 2) to an older (1.2±0.4, [36]) and a more recent measurement (0.87±0.04, [30]), performed independently of the current investigation. The TIFR 3d 4 D average lifetime [30] was determined using the line at 4119 A • and an O II 250 keV beam and subsequently performing ANDC analysis.…”

“…It is worth noting that, when the TIFR experiment was performed at beam energies of 334 keV, the lifetime for the 3d 4 D levels was estimated to be 3.8ns [30], a rather high value consistent with the results reported in [32] (Table 2). ANDC analysis has not been performed in the rest of the experimental studies ( [36], [24], [25]) in Table 2. The high lifetimes for the 3d 4 D levels, reported in early experiments ( [24] and [25]) have been discussed in [36], where it is noted that "mean lives measured in the visible or nearby regions in the early years of beamfoil spectroscopy should be treated with some caution".…”

“…ANDC analysis has not been performed in the rest of the experimental studies ( [36], [24], [25]) in Table 2. The high lifetimes for the 3d 4 D levels, reported in early experiments ( [24] and [25]) have been discussed in [36], where it is noted that "mean lives measured in the visible or nearby regions in the early years of beamfoil spectroscopy should be treated with some caution". In the subsequent measurement reported in [36], a decay channel in the VUV region has been used and the refined results obtained support the argument for a low average lifetime for the 3d 4 D levels ( Table 2).…”

Energy levels, radiative rates, and excitation rates for transitions in O IV

“…Also, although Nahar listed her calculated lifetimes for these two levels as being in agreement with the measurements of Pinnington et al (1978), this is not the case. Pinnington et al have measured the lifetimes for the 2s 2 3p 2 P • levels and not for the 2s2p( 3 P • )3s 2 P…”

“…In Table 4 we compare our calculated lifetimes for the lowest 25 levels of O iv with the available theoretical (Nahar 1998;Safronova et al 1999;Tachiev & Froese-Fischer 2000) and experimental (Pinnington et al 1974(Pinnington et al , 1978Ishi et al 1985) results. Lifetimes for all the listed levels are available only from the mchf calculations of Tachiev & Froese-Fischer which generally agree within ∼20% with our results.…”