Electromagnetic spectra, vibrational

Many characteristic molecular vibrations occur at frequencies in the infrared portion of the electromagnetic spectrum. We routinely analyze polymers by measuring the infrared frequencies that are absorbed by these molecular vibrations. Given a suitable calibration method we can obtain both qualitative and quantitative information regarding copolymer composition from an infrared spectrum. We can often identify unknown polymers by comparing their infrared spectra with electronic libraries containing spectra of known materials. 

The objective of this first part of the book is to explain in a chemically intelligible fashion the physical origin of microwave-matter interactions. After consideration of the history of microwaves, and their position in the electromagnetic spectrum, we will examine the notions of polarization and dielectric loss. The orienting effects of the electric field, and the physical origin of dielectric loss will be analyzed, as will transfers between rotational states and vibrational states within condensed phases. A brief overview of thermodynamic and athermal effects will also be given. 

Near-infrared Spectroscopy. Near-infrared spectroscopy (NIRS) uses that part of the electromagnetic spectrum between the visible and the infrared. This region has the advantage that the instrumentation is nearest to visible instrumentation. Signals in the near-infrared come not from the fundamental vibrations of molecules but from overtones. As... 

Absorption of radiation in the infrared region of the electromagnetic spectrum results in changes in the vibrational energy of molecules. Energy changes are typically 6 x 103 to 42 x 103J mol-1, which corresponds to 250-... 

Absorption of radiation in the radio-frequency, RF, region of the electromagnetic spectrum can be observed for those nuclei which are considered to spin about their own axes. The energy changes are associated with the orientation of the nuclear axis in space relative to an external applied magnetic field and are of the order of 0.1 J moH, 10-600 MHz (50 cm-30 m or 3 x 1(M to 2 x 10 2 cm1). This is considerably smaller than the energy changes associated with vibrational and electronic transitions (pp. 364, 378). 

Close to this limit the displacements of the two types of atom have opposite sign and the two types of atom vibrate out of phase, as illustrated in the lower part of Figure 8.10. Thus close to q = 0, the two atoms in the unit cell vibrate around their centre of mass which remains stationary. Each set of atoms vibrates in phase and the two sets with opposite phases. There is no propagation and no overall displacement of the unit cell, but a periodic deformation. These modes have frequencies corresponding to the optical region in the electromagnetic spectrum and since the atomic motions associated with these modes are similar to those formed as response to an electromagnetic field, they are termed optical modes. The optical branch has frequency maximum at q = 0. As q increases slowly decreases and... 

Infrared spectroscopy an analytical technique that quantifies the vibration (stretching and bending) that occurs when a molecule absorbs (heat) energy in the infrared region of the electromagnetic spectrum. 

Infrared spectroscopy has proven to be a very informative and powerful technique for the characterization of zeolitic materials. Most infrared spectrometers measure the absorption of radiation in the mid-infrared region of the electromagnetic spectrum (4000-400 cm or 2.5-25 xm). In this region of the spectrum, absorption is due to various vibrational modes in the sample. Analysis of these vibrational absorption bands provides information about the chemical species present. This includes information about the structure of the zeolite as well as other functional... 

Infrared radiation comprises that part of the electromagnetic spectrum that lies between microwaves and visible light (see p. 6). When it is absorbed by organic compounds, the energy is sufficient to cause the bonds within the molecules to vibrate, but not enough to break the bonds. 

The turbulent years just before the outbreak of World War I marked the point at which the Esoteric Tradition and Science were briefly espoused as Linda Henderson concludes, as an example of the supersensible vibrations of the electromagnetic spectrum, x-rays offered contemporary occultists a scientific rationale for phenomena such as clairvoyance as well as telepathy.. . . X-rays and radioactivity had made it impossible for the layman to think any longer of matter as solid and impenetrable or of space as a void. And, according to Henderson s most recent appraisal (1998),... 

Consider the line frequencies of an electronic transition. The quantity T e Tf is some constant for the pair of electronic states involved, and simply determines which region of the electromagnetic spectrum the transition falls. The positions of the vibrational bands are determined by... 

ABSORPTION BAND. A range of wavelengths (or frequencies) in the electromagnetic spectrum within which radiant energy is absorbed by a substance. When the absorbing substance is a polyatomic gas, an absorption band actually is composed of a group of discrete absorption lines, which appear to overlap. Each line is associated with a particular mode of vibration or rotation induced in a gas molecule by the incident radiation. The absorption bands of oxygen and ozone are often referred to in the literature of atmospheric physics. 

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