Controlled orbital collapse

Another property of atoms which is sensitive to the conditions in the outer reaches of the atomic field is of course orbital collapse, which can be controlled as described in section 5.23. This has led Golovinskiy et al. [480] to consider whether a strong laser field could be used to precipitate orbital collapse, and to propose an experiment in which dynamic collapse at the Rabi frequency could be detected by X-ray spectroscopy of the irradiated sample. 

We have emphasised the distinction between localised and itinerant states. Under certain circumstances (governed by atomic properties) a given orbital is poised at the critical point where it can become either one or the other for small changes in the environment of the atom. In solid state physics, this gives rise to a first-order Mott transition. In the present context, such a situation is closely related to the problem of controlled orbital collapse (section 5.23) if a solid is built up from free atoms with a double well potential and the corresponding orbitals in the outer well, these may hybridise easily, the external part of the orbital going into itinerant states. If one forms a solid from atoms with collapsed orbitals, then they remain localised. 

Diphenyl-3-p-tosyl-3,6-dihydro-2Ef-l, 3,4-oxadiazin-2-one (90) (Section 6.17.5.2) on treatment with t-butyllithium at — 78 °C undergoes an orbital symmetry controlled ring collapse of the resulting unstable l,3,4-oxadiazin-2-one (91) to 1,2-diphenylethyne <83TL4635>. 

Fig. 5.19. Controlled collapse, illustrated by a model calculation for the Cs atom which shows how the 4/ orbital can be made to transfer from one well into the other according to the excitation of the valence electron. The inset shows the 4d wavefunction, whose peak amplitude is very nearly coincident with the inner lobe of 4/, towards the centre of the inner well (after J.-P. Connerade [234]).

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