Final states, core-electron removal

Transition-metal and rare-earth atoms that contain partially occupied d or f valence subshells also give rise to spectral tine structure, often with very complicated multiplet splitting [2,27,28]. The spin-unpaired valence d or f electrons can undergo spin-orbit coupling with the unpaired core electron (remaining in the orbital from which the photoelectron was removed), producing multiple non-degenerate final states manifested by broad photoelectron peaks [2,27]. 

The thermo-chemical or the initial (neutral, un-ionized specimen with n elec-trons)-final (radiation beam ionized specimen with n — 1 electrons) states relaxation dominates the CLS [6, 7]. The energy required for removing a core electron from a surface atom is different from the energy required for a bulk atom. The surface atom is assumed as a Z -F 1 impurity sitting on the substrate metal of Z atomic number. The energy states of atoms at a flat surface or at a curved surface are expected to increase/decrease while the initial states of atoms in the bulk decreases/increase when the particle size is reduced. This mostly adopted mechanism creates the positive, negative, or mixed surface shift in theoretical calculations. 

The optically active electrons involve the 4f shell, buried deep within the Xe-core of electrons. Because of the shielding effect of the outer closed shells (5s25p6), the chemistry of each lanthanide is quite similar to the others. Thus, the separation of each rare earth, free from the others, has proven to be very difficult. The most stable valence state is Ln3+, where three (3) electrons (4fi and Gs ) have been removed. Most separations were accomplished in the 1800 s by repeated fractional crystallization. Sometimes, literally thousands of recrystallization steps were required before a reasonably pure product could be Isolated and demonstrated to be pure. A number of false starts have been recorded where the investigator thought he had a pure product, only to be shown that he did not. The first rare earth to be documented, gadoliniiun - Gd, was actually named around 1805. But, the product was later shown to be a mixture of rare earths. Gd was finally isolated in a pure form some 75 years later. It was named after the Swedish investigator, J. GadoUn (1794) who characterized the first rare earth ore. 

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