Transitions, inner electronic shell

Shorter-wavelength radiation promotes transitions between electronic orbitals in atoms and molecules. Valence electrons are excited in the near-uv or visible. At higher energies, in the vacuum uv (vuv), inner-shell transitions begin to occur. Both regions are important to laboratory spectroscopy, but strong absorption by make the vuv unsuitable for atmospheric monitoring. Electronic transitions in molecules are accompanied by stmcture... 

All d-block elements are metals (Fig. 1.63). Their properties are transitional between the s- and the p-block elements, which (with the exception of the members of Group 12) accounts for their alternative name, the transition metals. Because transition metals in the same period differ mainly in the number of /-electrons, and these electrons are in inner shells, their properties are very similar. 

The Group II elements each have two electrons in their outer energy shells, and the larger ones have an empty shell deep inside them. The transition series added electrons to the inner shell until it was completely filled. So, these last three transition elements are like Group II in construction, with the inner shell filled instead of empty, and two electrons in the outer shell. Those elements with filled shells and those with empty ones are the most stable. 

The reader may prefer to attach a reservation to this definition, making an exception of atoms in which the unpaired electron occupies an inner shell as in transition series elements. 

Inner electrons are usually excited by X-rays. Atoms give characteristic X-ray absorption and emission spectra, due to a variety of ionization and possible inter-shell transitions. Two relevant refined X-ray absorption techniques, that use synchrotron radiation, are the so-called Absorption Edge Fine Structure (AEFS) and Extended X-ray Absorption Fine Structure (EXAFS). These techniques are very useful in the investigation of local structures in solids. On the other hand, X-Ray Fluorescence (XRF) is an important analytical technique. 

Scandium is the first element in the fourth period of the transition elements, which means that the number of protons in their nuclei increases across the period. As with all the transition elements, electrons in scandium are added to an incomplete inner shell rather than to the outer valence shell as with most other elements. This characteristic of using electrons in an inner shell results in the number of valence electrons being similar for these transition elements although the transition elements may have different oxidation states. This is also why all the transition elements exhibit similar chemical activity. 

Free valencies of such an exciton nature may be significant in semiconductors, one component of which is a transition metal possessing an unfilled inner electron shell or a shell that can easily give up an electron. This may, perhaps, explain certain specific catalytic properties of such semiconductors. However, the role of Frenkel excitons in the phenomena of chemisorption and catalysis has been as yet investigated to a very small extent, and in the following we shall not consider free valencies of such an exciton origin. 

The colors in rare earth glasses are caused by the ion being dissolved and they behave uniquely because the 4 f electrons are deeply buried. Their colors depend on transitions taking place in an inner electronic shell while in other elements such as the transition metals, the chemical forces are restricted to deformation and exchanges of electrons within the outer shell. Since the rare earth s sharp absorption spectra are insensitive to glass composition and oxidation-reduction conditions, it is easy to produce and maintain definite colors in the glass making process. ( )... 

The remaining exceptions concern the lanthanide series, where samarium at room temperature has a particular hexagonal structure and especially the lower actinides uranium, neptunium, and plutonium. Here the departure from simple symmetry is particularly pronounced. Comparing these three elements with other metals having partly filled inner shells (transition elements and lanthanides), U, Pu, Np have the lowest symmetry at room temperature, normal pressure. This particular crystallographic character is the reason why Pearson did not succeed to fit the alpha forms of U, Pu, and Np, as well as gamma-Pu into his comprehensive classification of metallic structures and treated them as idiosyncratic structures . Recent theoretical considerations reveal that the appearance of low symmetries in the actinide series is intimately linked to the behaviour of the 5f electrons. 

Since the X-ray spectral lines come from the inner electrons of the atoms, die lines are not related to the chemical properties of the elements or to the compounds in which they may reside. Because the characteristics of die X-ray spectra are associated with energies released through transitions of electrons within the inner shells of the atom, the spectra are simple. Most practical X-ray fluorescence analysis involves the detection of radiation release through electron transitions from outer shells to the K shell (K spectra), outer shells to die L shell (L spectra) and, in very few cases, from outer shells to the M shell (M spectra). 

Radiative transitions with the participation of electrons from deep inner shells depend essentially on relativistic effects. This requires us to utilize relativistic operators and wave functions. Correlation effects are also significant but to a lesser extent. Superposition of configurations allows,... 

Let us turn our attention to the dominant recombination or deexcitation processes that follow the excitation of electrons from the inner shell or from the valence shell (Fig. 13). The first mode of deexcitation is the Auger process, which leads to further electron emission. The second mode of deexcitation may result in the emission of electromagnetic radiation and is commonly called X-ray fluorescence. In the Auger transition, the electron vacancy in an inner shell is filled by an electron from an outer band. The energy released by this transition is transferred to another electron in any... 

In summary, the dynamics of the electronic decay of inner-shell vacancies in a charged environment, such as created by interaction of a cluster with a high intensity FEL radiation, can be qualitatively different from the one induced by a low-intensity source. If the emitted electrons are slow enough to be trapped by the neighboring charges, the familiar exponential decay will be suppressed by quantum beats between the initial state and the quasi-continuum of discrete final states. Physically, the predicted oscillations correspond to creation of the initial vacancy due to the reflections of the emitted electron by the charged cluster potential and the subsequent inverse Auger transition. 

Interatomic Coulombic decay (ICD) is an electronic decay process that is particularly important for those inner-shell or inner-subshell vacancies that are not energetic enough to give rise to Auger decay. Typical examples include inner-valence-ionized states of rare gas atoms. In isolated systems, such vacancy states are bound to decay radiatively on the nanosecond timescale. A rather different scenario is realized whenever such a low-energy inner-shell-ionized species is let to interact with an environment, for example, in a cluster. In such a case, the existence of the doubly ionized states with positive charges residing on two different cluster units leads to an interatomic (or intermolecular) decay process in which the recombination part of the two-electron transition takes part on one unit, whereas the ionization occurs on another one. ICD [73-75] is mediated by electronic correlation between two atoms (or molecules). In clusters of various sizes and compositions, ICD occurs on the timescale from hundreds of femtoseconds [18] down to several femtoseconds [76-79]. 

It follows that once the total angular momentum of an ion, atom or molecule is known, so too is its magnetic moment. Most free atoms possess net angular momentum and therefore have magnetic moments, but when atoms combine to form molecules or solids, the electrons interact so that the resultant angular momentum is nearly always zero. Exceptions are atoms of the elements of the three transition series which, because of their incomplete inner electron shells, have a resultant magnetic moment. 

A possibility to extend this set comes from the use of an Electron-Cyclotron-Resonance-Ion-Trap (ECRIT), which will be realized using the cyclotron trap itself [22]. Here, hydrogen-like electronic atoms will be produced to obtain narrow calibration lines independent of an accelerator s pion beam. The radiative widths of light elements with Z k. 15 are of the order of a few 10 meV because of the absence of non-radiative inner-shell transitions. 

The complicated consequences of the absence of an electron in an inner shell are well-known from atomic line spectra. Thus, one may consider the red light emitted by neon atoms a perturbation of the two closely adjacent transitions in the yellow due to [Ne] 3p [Ne] 3s in sodium atoms, by removing a proton from... 

Another change Mendeleev made based on chemical analogy and intuition was placing iodine (T) after tellurium (Te), even though the atomic mass of iodine was less than tellurium. This anomaly, along with the difficulty of where to place the inner transition metals, were problems that would soon be definitively solved. At the time of the periodic table s construction, little was known of atomic structure. With further scientific discoveries such as the existence of protons and the existence of electronic shells, these mysteries were explained and placed into their current places in the periodic table. 

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