Matter, electromagnetic radiation

Have you ever wondered, Why is the sky blue There is no simple answer to this difficult question. To understand why the sky is blue, it is necessary to understand the nature and properties of matter and electromagnetic radiation and see the connections among matter, electromagnetic radiation, and color. We look to both art and chemistry for enlightenment... 

In the study of chemistry, the properties and composition of matter are investigated, along with the nature of electromagnetic radiation and how it affects matter. Electromagnetic radiation is radiant energy that exhibits wave properties and travels at the speed of light (when in a vacuum). 

The sample absorbs microwave radiation and converts the absorbed electromagnetic radiation to heat that the sample retains. Hence, the sample can be brought to a very high temperature without needing to heat the surroundings. Not all materials absorb microwave radiation. As with any matter-electromagnetic radiation interaction, three possibilities exist. The material can (1) reflect the radiation, (2) transmit the radiation with minimal attenuation, or (3) absorb the radiation. 

Gamma rays are completely different from neutrons for their action on the matter. Electromagnetic radiation as gamma rays knock electrons off atoms or molecules causing primary ionisation. This damage process was assessed in all tested organisms (Table 4). 

As discussed in more detail elsewhere in this encyclopaedia, many optical spectroscopic methods have been developed over the last century for the characterization of bulk materials. In general, optical spectroscopies make use of the interaction of electromagnetic radiation with matter to extract molecular parameters from the substances being studied. The methods employed usually rely on the examination of the radiation absorbed. 

The interaction of electromagnetic radiation with matter can be explained using either the electric field or the magnetic field. For this reason, only the electric field component is shown in Figure 10.2. The oscillating electric field is described by a sine wave of the form... 

The following sources present a theoretical treatment of the interaction of electromagnetic radiation with matter. 

The plane of polarization is conventionally taken to be the plane containing the direction of E and that of propagation in Figure 2.1 this is the xy plane. The reason for this choice is that interaction of electromagnetic radiation with matter is more commonly through the electric component. 

The vibrational motions of the chemically bound constituents of matter have fre-quencies in the infrared regime. The oscillations induced by certain vibrational modes provide a means for matter to couple with an impinging beam of infrared electromagnetic radiation and to exchange energy with it when the frequencies are in resonance. In the infrared experiment, the intensity of a beam of infrared radiation is measured before (Iq) and after (7) it interacts with the sample as a function of light frequency, w[. A plot of I/Iq versus frequency is the infrared spectrum. The identities, surrounding environments, and concentrations of the chemical bonds that are present can be determined. 

How do we know the composition of the sun and other stars How can we measure the temperature inside a flame so hot that any thermometer would melt How can we explore chemical reactions among molecules that are much too tiny to see directly Light allows us to do all these things. The study of matter with electromagnetic radiation is called spectroscopy. 

Let us now consider how electromagnetic radiation can interact with a particle of matter. Quantum mechanics (the field of physics dealing with... 

The relationship between electromagnetic radiation and matter (solids) is intertwined in the so-called space-time phenomenon. All solids emit photons, even yourself. The concept of absolute zero lies in the fact that no photons are emitted at 0° K. As the temperature rises, a spectrum of photon energies is emitted, as shown in the following diagram, given as 7.8.1. on the next page. 

Radiation, Ionizing—Any electromagnetic or particulate radiation capable of producing ions, directly or indirectly, in its passage through matter (see Radiation). 

The physical basis of spectroscopy is the interaction of light with matter. The main types of interaction of electromagnetic radiation with matter are absorption, reflection, excitation-emission (fluorescence, phosphorescence, luminescence), scattering, diffraction, and photochemical reaction (absorbance and bond breaking). Radiation damage may occur. Traditionally, spectroscopy is the measurement of light intensity... 

In the above rather simplified analysis of the interaction of light and matter, it was assumed that the process involved was the absorption of light due to a transition m - n. However, the same result is obtained for the case of light emission stimulated by the electromagnetic radiation, which is the result of a transition m -> n. Then the Einstein coefficients for absorption and stimulated emission are identical, viz. fiOT< n = m rt. 

Tlie problem of particular interest in physics and chemistry is concerned with the interaction of electromagnetic radiation, and light in particular, with matter. The electric field of the radiation can directly perturb an atomic or molecular system. Then, as in the Stark effect, the energy of interaction - the perturbation - is given by... 

In a vacuum (empty space), all forms of electromagnetic radiation propagate at a velocity of 300,000 km per second, when propagating through air, water, or any kind of matter, they interact with the matter and their velocity is reduced. Differences in the manner of interaction between different forms of radiation and different types of matter generally reveal information on the nature and the constituents of matter. 

The field of science that studies the interaction of electromagnetic radiation with matter is known as spectroscopy. Spectroscopic studies on the wavelength, the intensity of the radiation absorbed, emitted, or scattered by a sample, or how the intensity of the radiation changes as a function of its energy and wavelength, provide accurate tools for studying the composition and structure of many materials (Davies and Creaser 1991 Creaser and Davies 1988). 

Nuclear magnetic resonance spectroscopy is a technique that, based on the magnetic properties of nuclei, reveals information on the position of specific atoms within molecules. Other spectroscopic methods are based on the detection of fluorescence and phosphorescence (forms of light emission due to the selective excitation of atoms by previously absorbed electromagnetic radiation, rather than to the temperature of the emitter) to unveil information about the nature and the relative amount specific atoms in matter. 

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