Light, electromagnetic radiation

Fig. 3—Measurement of surface by HDI surface reflectance analyzer. In electromagnetic radiation (light), the polarization direction is defined as the direction of the electric field vector. The incident polarization of the light can be controlled. The instrument uses a variety of detectors to analyze the reflected polarization state of the light. (U.S. Patent 6,134,011). (a) Plane of the disk The SRA uses a fixed 60 degree (from the surface normal) angle of incidence. The plane of incidence is the same as the paper plane (b) Pit on a surface detected by reflected light channels of HDI instrument (c) Scratches on disk surface measured by HDI surface reflectance analyzer (d) Particles on the surface of disk detected by reflected light (black spot) and by scattered light (white spot) [8].

The various forms of spectroscopy find widespread application in kinetic studies. They are usually well suited for application to in situ studies of the characteristics of the reaction mixture. The absorption by a reacting system of electromagnetic radiation (light, microwaves, radio-frequency waves, etc.) is a highly specific property... 

We now consider the polarization induced by an oscillating electric field, such as that found in electromagnetic radiation (light), which can be expressed as... 

The interaction of molecules with electromagnetic radiation (light). 

Thus a plot of polarization as a function of the applied field is a straight line whose slope is the linear polarizability, a, of the optical medium (Figure lc). If the field oscillates with some frequency, (i.e., electromagnetic radiation, light), then the induced polarization will have the same frequency if the response is instantaneous (Figure la). Polarization is a vector quantity with both direction and magnitude. 

Today, organic chemists rely on an array of very powerful instruments that enable them to identify compounds in much less time. With use of these instruments, it is often possible to determine the structure of an unknown compound in less than an hour. Three of the most powerful techniques are presented in this and the following chapters. They are infrared spectroscopy and two related techniques proton and carbon-13 nuclear magnetic resonance spectroscopy. Spectroscopy is the study of the interaction of electromagnetic radiation (light) with molecules. 

Electromagnetic spectrum (Section 13.3) The range of electromagnetic radiation (light), from very energetic cosmic rays to low-energy radio waves. 

Spectroscopy (Chapter 13) The study of the interaction of electromagnetic radiation (light) with molecules. 

The mass spectrometer is now widely accepted as a crucial analytical tool for organic molecules in the pharmaceutical industry. Although usually treated as a spectroscopic technique, it does not rely on the interaction with electromagnetic radiation (light, infrared, etc.) for the analysis. Rather it is a micro-chemical technique relying on the production of characteristic ions in the gas phase, followed by the separation and acquisition of those ions. By its operation, it destroys the sample unlike other techniques, such as nuclear magnetic resonance (NMR), infrared (IR) and Raman/UV spectroscopies. Nonetheless, mass spectrometry is so sensitive that molecular weight and structural information can be provided on very small samples (attomolar (10" molar) quantities). 

We should begin by pointing out the distinction between radiation used in nuclear med-icine/radiopharmaceuticals (more akin to the other topics of this chapter) and electromagnetic radiation (light of different wavelengths). 

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