Helium fine structure splitting

Table 9. Comparison of theory and experiment for the fine structure splittings of helium 2 3Pj. Units are MHz...

In this paper we modify and extend this approach in several ways. In particular, we consider the magnetic fine structure effects in the presence of a uniform electric field F for ls2p Pj- excited states of helium. We introduce two separate differential polarizabihties to describe the quadratic part of the electric field splitting and three differential hyperpolarizabilities to describe the terms the order of in the fine-structure splitting of the atomic multiplet s2p Pj. We have developed a calculational approach that allows correct estimation of potential contributions due to continuum spectra to the dipole susceptibilities j3 and 7. In the next section we briefly outline our method. The details of the calculations of the angular and radial matrix elements have been described elsewhere [8,9] and are omitted here for brevity. Atomic units are used throughout. 

ESR spectra were recorded from 0 to 10,000 G at 110 K and 298 K and at several different power levels. The only ESR absorption observed was near g - 2. No fine structure splitting was observed. These experiments will be repeated a liquid helium temperatures In the near future In our laboratory. 

Yan, Z.-C., Drake, G. W. F. (1995). High Precision Calculation of Fine Structure Splittings in Helium and He-Like Ions. Phys. Rev. Lett. 74(24), 4791 794. 

The splitting of triplet terms of helium is unusual in two respects. First, multiplets may be inverted and, second, the splittings of the multiplet components do not obey the splitting rule of Equation (7.20). For this reason we shall discuss fine structure due to spin orbit coupling in the context of the alkaline earth atomic spectra where multiplets are usually normal and... 

At present, five experimental measurements for the 23P splittings are available all but the first [6] are from groups still active and working at helium FS measurements [4,7,8,9,10,11]. Although these experiments use different approaches to measure the fine structure, ranging from microwave spectroscopy in the 23P levels [6,9,10] to frequency difference of the 23,S —> 23P optical transitions [4,7,8,11], helium spectroscopy at 1083 nm is always present (see Fig. 1). A detailed description of all related experiments is out of the scope of this paper, and we will confine the discussion to our measurement [4], and briefly, to other measurements to compare with it. 

Our target is to develop a theory for the Lamb shift and the fine structure in these two atomic systems. Eventually we need to determine the 2s — 2pi/2 splitting in the helium ion (for comparison with the experiment [6]), difference of the Lamb shifts ER(2s) — ER(3s) in 4He+ (for the project [7]) and the 2p3/2 — 2s interval in hydrogen-like nitrogen. The difference mentioned is necessary [12,1] if one needs to compare the results of the Lamb shift (n = 2) measurement [6] and the 2s — 3s experiment. 

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