Spectroscopy electromagnetic mechanism

Schatz GC, Van Duyne RP. Electromagnetic mechanism of surface-enhanced spectroscopy. In Chalmers JM, Griffiths PR (Eds), Handbook of Vibrational Spectroscopy, Vol. 1. John Wiley Sons, Ltd, Chichester, 2002, pp. 759-774. 

Q. C. Schatz and R. P. Van Duyne, Electromagnetic mechanism of surfiuse-enhanced spectroscopy, in ... 

In absorption spectroscopy a beam of electromagnetic radiation passes through a sample. Much of the radiation is transmitted without a loss in intensity. At selected frequencies, however, the radiation s intensity is attenuated. This process of attenuation is called absorption. Two general requirements must be met if an analyte is to absorb electromagnetic radiation. The first requirement is that there must be a mechanism by which the radiation s electric field or magnetic field interacts with the analyte. For ultraviolet and visible radiation, this interaction involves the electronic energy of valence electrons. A chemical bond s vibrational energy is altered by the absorbance of infrared radiation. A more detailed treatment of this interaction, and its importance in deter-... 

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... 

One branch of chemistry where the use of quantum mechanics is an absolute necessity is molecular spectroscopy. The topic is interaction between electromagnetic waves and molecular matter. The major assumption is that nuclear and electronic motion can effectively be separated according to the Born-Oppenheimer approximation, to be studied in more detail later on. The type of interaction depends on the wavelength, or frequency of the radiation which is commonly used to identify characteristic regions in the total spectrum, ranging from radio waves to 7-rays. 

Even at the highest fields, the NMR experiment would not be practicable if mechanisms did not exist to restore the Boltzmann equilibrium that is perturbed as the result of the absorption of electromagnetic radiation in making an NMR measurement. These mechanisms are known by the general term of relaxation and are not confined to NMR spectroscopy. Because of the small magnitude of the Boltzmann excess in the NMR experiment, relaxation is more critical and more important in NMR than in other forms of spectroscopy. 

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... 

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