Accurate oscillator strengths for neutral helium

Abstract

With use of variational wave functions, oscillator strengths have been calculated for all the al-lo~ed transitions between the states n 'S, n 'I', n 'D, n S, n 'I', and n D, n &9, in neutral helium, with an estimated accuracy of better than 1% for most of the transitions and better than 0.1% for about a third of the transitions. The error estimate is based on numerical convergence as the number of expansion terms in the wave function is increased. By use of rapidly converging trial functions consisting of two sets of Hylleraas-type basis functions differing in the values of nonlinear parameters, the expansion lengths required are kept moderate (at most 140 terms). A discussion is given about the completeness of the Hylleraas-type basis.

Relativistic Calculations of Transition Amplitudes in the Helium Isoelectronic Sequence

“…These benchmark calculations were confirmed and extended by Kono and Hattori [22] and by Sandars and Knight [23]. Most recently, Cann and Thakkar [24] have carried out high-precision variational calculations of oscillator strengths for S − P and P − D transitions for ions in the range Z = 2 − 10.…”

Radiative Lifetimes of Eu i , ii , and iii and Transition Probabilities of Eu i

“…These include lifetimes for levels in Be i (Weiss 1995), Be ii (Yan, Tambasco, & Drake 1998), and Fe ii (Guo et al 1992;Biémont et al 1991), covering the range from 1.8 to 8.8 ns. He i lifetimes are measured in the range 95-220 ns (Kono & Hattori 1984). The Fe ii lifetimes are from very accurate (uncertainty <AE2%) experimental work using the laser-fast beam method, while the Be i, ii and He i lifetimes are from theoretical oscillator strengths (uncertainties AE2%, AE0.01%, and <AE0.1%, respectively).…”

Experimental Radiative Lifetimes, Branching Fractions, and Oscillator Strengths for Laiiand a New Determination of the Solar Lanthanum Abundance

“…Accurate calculations for Be I (Weiss 1995) and Be II (Yan, Tambasco, & Drake 1998) provide cross-checks for lifetimes in the range of 1.8È8 ns. Accurate calculations for He I (Kono & Hattori 1984) provide cross-checks for lifetimes in the range of 95È220 ns. The La II lifetimes reported here have overall uncertainties equal to the greater of^5% or^0.2 ns.…”