Electronic transitions in an atom

A number of characteristic X-rays can be emitted from an atom if a number of inner shell electrons have been knocked out by high energy particles. The individual characteristic X-rays are marked Ka, Kf5... as mentioned in Chapter 2. It seems that there are many possible ways in which outer shell electrons can fill inner shell vacancies however, the possibilities are limited and such electron transitions in an atom are controlled by the selection rules. 

Fig. 1-7 Electronic transitions in an atom (schematic). Emission processes indicated by arrows.

An electronic singlet S state (L = 0) does not interact at all with a magnetic field. In Figure 2, the Zeeman effect on an electronic transition between an atomic S state and a P state with zero spin is sketched. Radiative electric dipole transitions can occur between all three Zeeman sublevels of the P state and the S state, thus giving rise to three (closely spaced) spectral lines. 

Let us consider the flux F, per unit of time, through a sphere S of large radius, of the Poynting vector of the field, created by the transition current between two states, of an electron bound in an atom. If we consider the energy E released at each transition, the ratio F/E gives the number of transitions per... 

When the light of quantum energy hv falls on an electron, bound in an atom, whose energy is E > 0, a quantum may be absorbed and the electron jumps into a state of energy E2 = E + hv. The energy E belongs to the discrete spectrum and E2 may belong to the discrete (bound-bound transition) or to the continuous spectrum (photoeffect). 

AES involves the measurement of electromagnetic radiation emitted from atoms. Both qualitative and quantitative data can be obtained from this type of analysis. In the former case, the identity of different elements reflects the spectral wavelengths that are produced, while in the latter case, the intensity of the emitted radiation is related to the concentration of each element. Atomic spectra are derived from the transition of electrons from one discrete electron orbital in an atom to another. These spectra can be understood in terms of the Bohr atomic model. 

Atomic vapor-absorption bands can be used to produce a high-performance notch filter [57-65]. As its name suggests, this type of filter relies on the absorption of specific wavelengths by electron orbital transitions in an atomic vapor. The filter is based on a metal vapor (e.g., rubidium [65]), which is often held in a transparent glass cell. Such filters can produce fair attenuation (3-5 optical density) over a very narrow bandwidth (less than 1 cm ) [63]. Their principal drawbacks are their relative complexity, their many closely spaced absorption peaks that can interfere with the data of interest, and the fact that the absorption peaks are not necessarily coincident with common laser wavelengths. Because the filter s absorption bands are so extremely narrow, if the laser shifts frequency even minutely, it will fall outside the absorption peak and will not be blocked. These challenges reduce the general applicability and attractiveness of this type of filter for Raman systems. 

Electronic spectroscopy is the study of transitions, in absorption or emission, between electronic states of an atom or molecule. Atoms are unique in this respect as they have only electronic degrees of freedom, apart from translation and nuclear spin, whereas molecules have, in addition, vibrational and rotational degrees of freedom. One result is that electronic spectra of atoms are very much simpler in appearance than those of molecules. 

If ionization of a core level X in an atom A in a solid matrix M by a primary electron of energy Ep gives rise to the current Ij (XYZ) of electrons produced by the Auger transition XYZ, then the Auger current from A is... 

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