Electromagnetic energy spectrum

Figure 11.2 Electromagnetic energy spectrum. Rotational and vibrational motions occur in the infrared range. Ionization and covalent bond breakage occur at higher energies in the UV and X-ray range. Nuclear spins are affected at much lower energies (labeled NMR). Source O Howarth, Theory of Spectroscopy an Elementary Introduction, Wiley, New York, 1973.

Wavelengths in angstroms FIGURE 40.15 The electromagnetic energy spectrum. 

Infrared, ultraviolet, and nuclear magnetic resonance spectroscopies differ from mass spectrometry in that they are nondestructive and involve the interaction of molecules with electromagnetic energy rather than with an ionizing source. Before beginning a study of these techniques, however, let s briefly review the nature of radiant energy and the electromagnetic spectrum. 

Direct Photolysis. Direct photochemical reactions are due to absorption of electromagnetic energy by a pollutant. In this "primary" photochemical process, absorption of a photon promotes a molecule from its ground state to an electronically excited state. The excited molecule then either reacts to yield a photoproduct or decays (via fluorescence, phosphorescence, etc.) to its ground state. The efficiency of each of these energy conversion processes is called its "quantum yield" the law of conservation of energy requires that the primary quantum efficiencies sum to 1.0. Photochemical reactivity is thus composed of two factors the absorption spectrum, and the quantum efficiency for photochemical transformations. 

The spectral resolution of the most monochromatic laser yet devised, expressed as frequency of the laser emission divided by the laser linewidth, is approximately 5 x 10. The laser in question is a special-purpose He-Ne laser with a nominal wavelength of 632.8 nm (15,308 cm l or 4.74 x 10 Hz in frequency units) and a linewidth of 7 to 10 Hz. It is difficult to grasp the physical significance of this degree of resolution. One illustration is that, if the spectrum of this laser were displayed on chart paper such that the zero of electromagnetic energy were located at the sun and 15,308 cm l were located at the orbit of Earth, the width of the peak representing the output of the laser would be 3 millimeters. 

The origin and cause of acceleration of cosmic rays is somewhat uncertain, but the power-law energy spectrum suggests some kind of electromagnetic process... 

The microwave acoustic effect may be defined as the auditory perception of microwave radiation which is a form of electromagnetic energy which occupies the part of spectrum between ordinary radio waves and infrared and optical waves. This definition may... 

It was the analysis of the line spectrum of hydrogen observed by J. J. Balmer and others that led Neils Bohr to a treatment of the hydrogen atom that is now referred to as the Bohr model. In that model, there are supposedly allowed orbits in which the electron can move around the nucleus without radiating electromagnetic energy. The orbits are those for which the angular momentum, mvr, can have only certain values (they are referred to as quantized). This condition can be represented by the relationship... 

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