L shell

A common example of an Auger process involves the ejection of a photoelectron, as shown in Figure 8.23, from the K shell (i.e. a lx electron), with energy E, which is not considered further. Following the ejection of a if electron it is common for an electron from the L shell, specifically from fhe (or 2s) orbifal, fo fill fhe vacancy releasing an amounf of energy... 

X-Rays. If an x-ray is emitted, it has an energy, AE, equal to the difference in the binding energies of the two atomic shells, E — Ej. If the original hole is in the K shell, the x-ray is called a K x-ray if the hole is in the L shell it is an L x-ray. Because the hole can be filled by an electron from any of the several outer shells, x-ray spectra contain a large number of discrete lines. 

Figure 5 Comparison of spectral profiles measured from a specimen of NiO using EDS and EELS. Shown are the oxygen K- and nickel L-shell signals. Note the difference in the spectral shape and peak positions, as well as the energy resolution of the two spectroscopies.

In these approximations for the K series the value 1 is subtracted from the atomic number Z to correct for the screening of the nuclei by the remaining K-shell electron. For the L series the screening effect of the two K-shell electrons and the seven remaining L-shell electrons must be taken into consideration by subtracting 7.4. 

Carbon has six electrons around the atomic core as shown in Fig. 2. Among them two electrons are in the K-shell being the closest position from the centre of atom, and the residual four electrons in the L-shell. TTie former is the Is state and the latter are divided into two states, 2s and 2p. The chemical bonding between neighbouring carbon atoms is undertaken by the L-shell electrons. Three types of chemical bonds in carbon are single bond contributed from one 2s electron and three 2p electrons to be cited as sp bonding, double bond as sp and triple bond as sp from the hybridised atomic-orbital model. 

If certain quanta suitable for the excitation of a line are absorbed without photon emission, a radiationless transition is likely. This transition is known as the Auger effect,39 and it may be thought to involve an absorption by the atom of the photon produced when the hole in the K shell is filled by an electron from one of the external shells such as the L shell. The absorption of this photon results in the ejection of a second electron from one of the shells to leave a doubly charged residue of what had been a normal atom. The atom in this condition is described by naming the two states in which the electron holes are to be found e.g., the atom is in the LL or LM or LN state. An atom in such a state is, of course, vastly different from the usual divalent cation. 

Capture, Electron—A mode of radioactive decay involving the capture of an orbital electron by its nucleus. Capture from a particular electron shell, e.g., K or L shells, is designated as "K-electron capture" or "L-electron capture."... 

Table l.l Shell Structure of the Atoms of the First 20 Elements... 

What is the maximum number of electrons that can occupy the K shell the L shell ... 

Ans. The K shell, the first shell, can hold a maximum of two electrons. The L shell can hold a maximum of eight electrons. 

As yet, this marks no radical departure from the classical picture of orbits, but with the 2p level (the continuation of the L shell) a difference becomes apparent. Theory now requires the existence of three 2p orbitals (quantum numbers n = 2, Z = 1, with m = +1,0, and... 

The localized quantities of the IGLO results allow separation of the influences of the different bonds, of the inner shells and of the lone pairs on the shielding of the resonance nuclei. It is evident from Table 1 that the SiX bonds with different substituents X do mainly contribute to the chemical shifts. On the other hand, the substituents X have distinct influences on the chemically unchanged parts of the molecules as in system II and on the inner L shell which, on their parts, influence the nuclear shielding, too. 

Bethe s formula requires that the velocity of the incident particle be much larger than that of the atomic electrons, a condition not easily fulfilled by the K-electrons except in the lightest elements. The required correction, called the shell correction, is denoted by subtracting a quantity C from the stopping number. In the penetration of high-Z material, even L-shell correction may be required. In that case, C denotes the sum total of all shell corrections. The subject of shell correction has been extensively treated by several authors, and various graphs and formulas are available for its evaluation (see, e.g., Bethe andAshkin, 1953). 

Carbon, chemical symbol C, has six protons and six electrons. Two electrons fill the inner K energy shell, and there are four electrons in its outer L shell. Since this is exactly halfway to the number eight, which would fill the outer shell, carbon has little tendency to gain or lose electrons. Instead, carbon usually combines by sharing electrons with two, three, or four other atoms. 

The sharing of electrons fills the K shell for each hydrogen atom (2 electrons) and the L shell for the carbon atom (8 electrons). Opposite are two ways of showing how the atoms of the compound ethanol, C2Hr,OH (which is drinking alcohol), are connected to one another. Chemists usually use a dash to represent each pair of electrons shared between two atoms, instead of the dots used above. Each atom now has a filled outer shell. The hydrogens are each... 

The emission from copper is shown in Figure 2.66. The two prominent lines in the copper emission are termed the copper and K., lines. The transitions responsible are to the K shell, that with principal quantum number one, the 2s and 2p levels are referred to as the L shell, etc. The Greek letters indicate from where the transition originates the 2p Is transition gives the line and the 3p-> Is the line. Sometimes the line is split into a doublet as a result of exchange terms. 

Auger-L = L-shell Auger electron b ce-K = K-shell conversion electron yray c A = Equilibrium absorbed — dose constant... 

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