Electromagnetic radiation Absorption spectroscopy. Atomic

Spectroscopy The science of analyzing the spectra of atoms and molecules. Emission spectroscopy deals with exciting atoms or molecules and measuring the wavelength of the emitted electromagnetic radiation. Absorption spectroscopy measures the wavelengths of absorbed radiation. 

Absorption spectroscopy records electromagnetic radiation (energy) as atoms absorb energy, and conversely emission spectroscopy records energy emitted during atomic transitions. 

The spectroscopy of solids is defined as the qualitative or quantitative measurement of the interaction of electromagnetic radiation (emr) with atoms or molecules in the solid state. The emr interacts as scattering, absorption, reflectance, or emission with solid matter. A variety of spectrometer configurations are used to optimize the measurements of electromagnetic radiation as it interacts with solid matter. This chapter provides an overview of... 

Spectroscopy is basically an experimental subject and is concerned with the absorption, emission or scattering of electromagnetic radiation by atoms or molecules. As we shall see in Chapter 3, electromagnetic radiation covers a wide wavelength range, from radio waves to y-rays, and the atoms or molecules may be in the gas, liquid or solid phase or, of great importance in surface chemistry, adsorbed on a solid surface. 

Atomic and Molecular Energy Levels. Absorption and emission of electromagnetic radiation can occur by any of several mechanisms. Those important in spectroscopy are resonant interactions in which the photon energy matches the energy difference between discrete stationary energy states (eigenstates) of an atomic or molecular system = hv. This is known as the Bohr frequency condition. Transitions between... 

Collision-induced absorption is a well developed science. It is also ubiquitous, a common spectroscopy of neutral, dense matter. It is of a supermolecular nature. Near the low-density limit, molecular pairs determine the processes that lead to the collision-induced interactions of electromagnetic radiation with matter. Collision-induced absorption by non-polar fluids is particularly striking, but induced absorption is to be expected universally, regardless of the nature of the interacting atoms or molecules. With increasing density, ternary absorption components exist which are important especially at the higher temperatures. Emission and stimulated emission by binary and higher complexes have also... 

The basis of NMR spectroscopy lies in the absorption of electromagnetic radiation at radiofrequencies by atomic nuclei.426 427 432-437 All nuclei with odd mass numbers (e.g., H, 13C, 15N, 170,19F, and 31P), as well as those with an even mass number but an odd atomic number, have magnetic properties. Absorption of a quantum of energy E = hv occurs only when the nuclei are in the strong magnetic field of the NMR spectrometer and when the frequency v of the applied electromagnetic radiation is appropriate for "resonance"... 

There are several reasons for starting this account with a discussion of electromagnetic radiation. Historically, it was in this area that the quantum theory first developed. It is easier here to understand the evidence for the theory, and to appreciate some of its paradoxical consequences, than it is in the quantum theory of matter. The applications of the light-quantum hypothesis, as it was first called, also provide key pieces of evidence for the quantization of energy in atoms and molecules. Studies of the absorption and emission of radiation—the field of spectroscopy—and of the effect of light on chemical reactions—photochemistry—are very important areas of modem chemistry, in which the quantum nature of radiation is crucial. 

Most other forms of spectroscopy do not involve emission of extra particles such as electrons, but the straightforward absorption or emission of photons. These processes increase or decrease the energy of an atom ex molecule, by an amount equal to the photon energy. The results all reinforce the conclusion of photoelectron spectroscopy that only discrete energy levels occur (see Fig. 1.12). For example, the line spectra of atoms, known since the early nineteenth century, only contain lines at certain well-defined wavelengths. The quantization of energy, not only in electromagnetic radiation but in material systems, is an inescapable conclusion rtf spectroscopy. 

Flame Atomic Absorption Spectroscopy FAAS is one of the oldest analytical techniques and continues to be used in the analysis of food products. The analysis is usually performed in an air-acetylene or a nitrous oxide-acetylene flame. The technique measures the absorbance of electromagnetic radiation by the free atoms produced at high temperamre (1000-4000 K) [6]. 

Concentrating on metalloenzymes, we have developed a strategy based on stopped flow X-ray absorption spectroscopy (XAS) to elucidate in detail the molecular mechanisms at work during substrate turnover (Fig. 4). Importantly, XAS provides local stmctural and electronic information about the nearest coordination environment surrounding the catalytic metal ion within the active site of a metalloprotein in solution. When the X-rays hit a sample, the electromagnetic radiation interacts with the electrons bound in the metal atom. The radiation can be scattered by these electrons, or it can be absorbed, thereby exciting... 

In this chapter, we discuss the basic principles that are necessary to understand measurements made with electromagnetic radiation, particularly those deeding with the absorption of UV, visible, and IR radiation. The nature of electromagnetic radiation and its interactions with matter are stressed. The next four chapters are devoted to. spectroscopic instruments (Chapter 25), molecular absorption spectroscopy (Chapter 26), molecular fluorescence spectroscopy (Chapter 27), and atomic spectroscopy (Chapter 28). 

Experimental study of the double layer is not limited to thermodynamics. A variety of spectroscopic methods have been applied to determine the structure and composition of the double layer. Two of these, namely, second-harmonic generation and vibrational sum frequency spectroscopy, have already been described in section 8.11. Other important techniques are based on the absorption of electromagnetic radiation when it is transmitted through or reflected at the interface. Finally, the scattering of X-rays and neutrons at interfaces has proven to be a valuable tool for obtaining atomic level information about the interface. In the following section some of these methods are outlined in more detail. 

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