Crystalline solids electromagnetic radiation

X-rays Electromagnetic radiation with wavelengths ranging between 10"10 and lO cm. X-rays diffraction A physical method for determining the structure of crystalline solids by exposing the solids to X-rays and then studying the varying intensity of the difracted rays due to interference effects. 

Fig. 7.2. Diffraction of electromagnetic radiation by planes of atoms in a crystalline solid.

The model fundamental to all analyses of vibrational motion requires that the atoms in the system oscillate with small amplitude about some defined set of equilibrium positions. The Hamiltonian describing this motion is customarily taken to be quadratic in the atomic displacements, hence in principle a set of normal modes can be found in terms of these normal modes both the kinetic energy and the potential energy of the system are diagonal. The interaction of the system with electromagnetic radiation, i.e. excitation of specific normal modes of vibration, is then governed by selection rules which depend on features of the microscopic symmetry. It is well known that this model can be worked out in detail for small molecules and for crystalline solids. In some very favorable simple cases the effects of anharmonicity can be accounted for, provided they are not too large. 

X ray Electromagnetic radiation of shorter wavelength X-ray diffraction An analytical technique used to than ultraviolet radiation (10-11 m to 10-9 m or 0.01 nm determine the structures of crystalline solids. 

X-rays are electromagnetic radiation of wavelength about lA (10 m), which is about the same size as an atom. They occur in that portion of the electromagnetic spectrum between gamma rays and the ultraviolet. The discovery of X-rays in 1895 enabled scientists to probe crystalline structure at the atomic level. X-ray diffraction has been in use in two main areas for the fingerprint characterization of crystalline materials and the determination of their structure. Each crystalline solid has its unique characteristic X-ray powder pattern, which may be used as a "fingerprint" for its identification. Once the material has been identified. X-ray... 

From the point of view of analytical control of medicinal products, this domain is the most used. At the base of absorption is being generated electromagnetic radiation in this area spectral transitions are the vibrations of individual molecules or of crystalline network (if the sample examined is solid). Show effects such transitions caused by the vibrations of individual molecules provides information about molecular structure of the sample examined, and show effects such crystalline network to identify a particular forms of crystallization of the substance of interest. 

In order to experimentally ascertain the space group and ultimate 3-D structure of a crystalline solid, one must impinge the crystal with high-energy electromagnetic radiation. For instance, when X-rays interact with a crystalline solid, the incoming... 

How do we determine these regular arrangements As with spectroscopy, we can use electromagnetic radiation as a probe. But rather than absorbing or emitting radiation, crystalline solids can diffract radiation under certain conditions. These conditions are dictated by the structure of the crystal, and there is a simple rule for relating the diffraction effect to the crystal s structure. 

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