Electromagnetic radiation and atomic spectra

The wavelength of wave X has double the value of the wavelength of wave Y. As both waves travel at the same velocity (c = 3 X 10 m s ), then twice as many wavelengths of wave Y will pass position A every second compared to wave X. This means that the frequency of wave Y is twice that of wave X. 

DUAL NATURE OF ELECTROMAGNETIC RADIATION WAVES AND PARTICLES 

Electromagnetic radiation can be absorbed or emitted. The absorption of ultraviolet radiation by our skin may cause sunburn. When we cook food in a microwave oven, the absorption of microwave radiation by the water in the food causes the water molecules to vibrate, generating heat that cooks the food. However, when electromagnetic radiation is absorbed or emitted by matter, it behaves more like a stream of particles than as a wave motion. These particles are called photons and so electromagnetic radiation can be considered both as a stream of photons and as waves with characteristic properties, such as wavelength (1) and frequency (/). Therefore we say that electromagnetic radiation has a dual nature wave motion and streams of photons. 

Electromagnetic radiation that has a short wavelength and high frequency, such as gamma rays, is at the high energy end of the electromagnetic spectrum. 

Radio waves and other radiation with a long wavelength and low frequency are at the low energy end of the electromagnetic spectrum. 

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Inorganic and physical chemistry Electromagnetic radiation and atomic spectra... 

But if, on the basis of these conceptions and the classical principles, we now attempt to develop a mechanical theory of the atom, we encounter the following fundamental difficulty a system of moving electric charges, such as is pictured in this model, would continually lose energy owing to electromagnetic radiation and must therefore gradually collapse. Further, all efforts to deduce the characteristic structure of the series spectra on the basis of the classical laws have proved fruitless. 

Read materials assigned by your instructor on electromagnetic radiation, quantization of energy, and atomic spectra. 

Spectroscopy The science of analyzing the spectra of atoms and molecules. Emission spectroscopy deals with exciting atoms or molecules and measuring the wavelength of the emitted electromagnetic radiation. Absorption spectroscopy measures the wavelengths of absorbed radiation. 

Most of what we know about the structure of atoms and molecules has been obtained by studying the interaction of electromagnetic radiation with matter. Line spectra reveal the existence of shells of different energy where electrons are held in atoms. From the study of molecules by means of infrared spectroscopy we obtain information about vibrational and rotational states of molecules. The types of bonds present, the geometry of the molecule, and even bond lengths may be determined in specific cases. The spectroscopic technique known as photoelectron spectroscopy (PES) has been of enormous importance in determining how electrons are bound in molecules. This technique provides direct information on the energies of molecular orbitals in molecules. 

Electromagenetic Radiation. Atomic and Molecular Energy. The Absorption and Emission of Electromagnetic Radiation. The Complexity of Spectra and the Intensity of Spectral Lines. 

Chapter 4, presents details of the absorption and reflectivity spectra of pure crystals. The first part of this chapter coimects the optical magnimdes that can be measured by spectrophotometers with the dielectric constant. We then consider how the valence electrons of the solid units (atoms or ions) respond to the electromagnetic field of the optical radiation. This establishes a frequency dependence of the dielectric constant, so that the absorption and reflectivity spectrum (the transparency) of a solid can be predicted. The last part of this chapter focuses on the main features of the spectra associated with metals, insulators, and semiconductors. The absorption edge and excitonic structure of band gap (semiconductors or insulator) materials are also treated. 

Binary and ternary spectra. We will be concerned mainly with absorption of electromagnetic radiation by binary complexes of inert atoms and/or simple molecules. For such systems, high-quality measurements of collision-induced spectra exist, which will be reviewed in Chapter 3. Furthermore, a rigorous, theoretical description of binary systems and spectra is possible which lends itself readily to numerical calculations, Chapters 5 and 6. Measurements of binary spectra may be directly compared with the fundamental theory. Interesting experimental and theoretical studies of various aspects of ternary spectra are also possible. These are aimed, for example, at a distinction of the fairly well understood pairwise-additive dipole components and the less well understood irreducible three-body induced components. Induced spectra of bigger complexes, and of reactive systems, are also of interest and will be considered to some limited extent below. 

Real gases. This book deals with the spectra of real (as opposed to ideal) gases, that is gases composed of real atoms or molecules which interact not only with electromagnetic radiation, but also with the other atoms and molecules of the gas. 

Atomic line spectra arise because electromagnetic radiation occurs only in discrete units, or quanta. Just as light behaves in some respects like a stream of small particles (photons), so electrons and other tiny units of matter behave in some respects like waves. The wavelength of a particle of mass m traveling at a velocity v is given by the de Broglie equation, A = h/mv, where h is Planck s constant. 

The vibrational processes in molecules are also reflected in the Raman spectra (Spiro, 1987, 1988). When the substance is irradiated at a frequency far from the frequency of its absorption, additional (satellite) lines may appear in the scattering light. The origin of such lines is accounted for by the fact that during the interaction of electromagnetic radiation, the molecule part of the radiant energy is transferred to the excited vibrational levels and part of the energy is released from the excited levels. In metalloenzymes and in substrate-enzyme and inhibitor-enzyme complexes the active sites incorporate only a small part of the macromolecular atoms. 

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