Electromagnetic spectrum atomic emission spectroscopy

Atomic emission spectroscopy is one of the oldest instrumental techniques used for chemical analysis. It is used to study the transitions between electronic energy levels in atoms or ions. These energy differences are usually in the visible region (400-700 nm) of the electromagnetic spectrum, but if the energy difference is larger, then the transitions may lie in the ultraviolet region. 

Molecular spectroscopy is the experimental process of measuring which frequencies of radiation are absorbed or emitted by a particular substance and then attempting to correlate patterns of energy absorption or emission with details of molecular structure. Table 12.3 summarizes the regions of the electromagnetic spectrum of most interest to us and the relationships of each to changes in atomic and molecular energy levels. 

In vacuum ultraviolet photoelectron spectroscopy (UPS), the sample atom or molecule is exposed to radiation in the vacuum ultraviolet region of the electromagnetic spectrum. A readily available source of radiation is the helium discharge lamp, whieh produces a sharp Hel line at 21.2 eV. Since the energy required for photoionization of sets of valence electrons is in the vicinity of 6 eV to this energy, we obtain a polyenergetic emission of electrons described by the Einstein relation... 

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