Beryllium forbidden

C08-0054. The following are hypothetical configurations for a beryllium atom. Which use nonexistent orbitals, which are forbidden by the Pauli principle, which are excited states, and which is the... 

Both Lithium-5 and Helium-5 have the impossible half-lives of 10 to the minus 21 seconds. Hence, in the primordial soup, the only way to get into something heavier than helium was to have a collision between a couple of the relatively scarcer heavy nuclei, or to have a three body collision. Both of these would be extremely rare events, statistically. And if a few got through, there was another forbidden barrier at mass 8, since Beryllium-8 has a half life of 10 to the minus 16 seconds. So everything had to wait for a few suns to burn down so that they could process enough helium into heavy atoms, to achieve some nuclear chemistry that was not allowed in the early history of the universe. 

Figure 2.5. The schematic spectrum of the states of the free gaseous beryllium atom showing on the left the orbital scheme with electron occupation and on the right half the term levels. One electron configuration can correspond to several terms. The allowed optical transition is indicated with a bold arrow and the forbidden transitions that correspond with weak absorption in the optical spectrum are indicated with thin arrows between the ground state and the excited states.

Predictions of [13] also include 2s 2p levels of some ions isoelectronic with O, N, C, B, Be, and Li. The elements Os, Ir, and Pt are not considered, but relevant data can be derived by interpolation. Isoelectronic trends in the n=2 —n=2 transition probabilities are sketched in [14] for boron-like ions by the relativistic parametric potential method and in [15] for beryllium-like ions by a 1/Z perturbation method. In a survey of the lithium-like sequence, Steiger reports spontaneous emission rates and energies for three forbidden transitions of lr + [16]. A relativistic model potential method was used by Gogava etal. for deriving the lowest 15 energy levels of all lithium-like ions [17]. 

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