Particle character, of light

Einstein insisted on the particle character of light. In the long wavelength limit of radio waves and alternating currents, the wave interpretation seemed to be the only possibility thongh. Concerning other types of EM radiation, it is easy to accept that y-rays are particles like a and p particles. In 1923, the American physicist Arthur Compton showed experimentally that electrons are scattered by x-rays. This experiment is very easy to interpret, if it is assumed that x-rays consist of particles. An interpretation in terms of waves is, in fact, also possible, but it had to wait for several decades. It was now concluded that Einstein was right in his proposal that x-rays consist of particles. Photon was accepted as a name for this elementary particle. 

Schrodinger s equation is widely known as a wave equation and the quantum formalism developed on the basis thereof is called wave mechanics. This terminology reflects historical developments in the theory of matter following various conjectures and experimental demonstration that matter and radiation alike, both exhibit wave-like and particle-like behaviour under appropriate conditions. The synthesis of quantum theory and a wave model was first achieved by De Broglie. By analogy with the dual character of light as revealed by the photoelectric effect and the incoherent Compton scattering... 

Quantum mechanics tells us that the forces of nature can manifest themselves as particles. Photons of light, for example, are the particles associated with the electromagnetic force. Such particles are not constituents of matter they have an entirely different character. The photons that are responsible for electromagnetic forces are never observed. They are emitted by one matter particle and absorbed by another before they can be detected. However, there is little doubt that these phenomena take place because there is ample indirect evidence that they do. 

Modern atomic theory received a shot in the arm when it was recognized that the individual atom has light absorption and emission spectra occurring at narrow lines of the spectrum at specific wavelengths, as opposed to the broad bands typical of the polyatomic molecules and compounds. Since the line spectrum of each element is characteristic of that element, atomic spectroscopy can be used for precise elementary analysis of many types of chemically simple and complex materials. These studies make use of the wave character of light, as well as light s particle character. 

The solution, proposed by Einstein, was that the discrete energy units, identified by Planck, correspond to quanta of light, called photons, which interact with electrons in the metal surface during direct collision. This dual wave/particle nature of light inspired de Broglie to postulate a similar behaviour for electrons. Experimental observation of electron diffraction confirmed the wave nature of electrons and firmly estabUshed the dual character of all quantum objects as mysterious reality. As the logical pictme of an entity, which is wave as well as particle, is hard to swallow, it has become fashionable to avoid all physical models of quantum events it is considered poor taste to contaminate the quantmn world with classical concepts. This noble idea of the so-called Copenhagen interpretation of quantmn theory has resulted in a probabilistic computational model that, not only defies, but denies comprehension. 

Louis Victor de Broglie (1892-) extended the dual character of light (wave and corpuscular) to matter. In 1924 he proposed that an electron in motion (as in a Bohr orbit) had a wave associated with it. C. J. Davisson, L. H. Germer, and G. P. Thomson found experimental evidence for this wave nature of particles in 1927 (Holum 1969, p. 37). 

The propagation of light in multiple scattering media is quantified usually on the level of radiative transfer or particle diffusion. Scattering, absorption, and emission are considered as independent statistical processes, and the consequences of wave character are either ignored, like polarization, or added as an additional parameter, like the phase function P(ji n) that describes the angular distribution of scattered... 

In this case the initial act of light absorption leads to the formation of an exciton, rather than a free electron or hole. Such an exciton, as it wanders through the crystal, may meet a lattice defect and annihilate on it, the energy of the exciton being utilized to ionize the defect, i.e., to transfer an electron or hole localized on the defect to the free state (the mechanism of Lashkarev-Juze-Ryvkin, see 90, 91). If such a defect is a foreign particle chemisorbed on the crystal surface, the result will be a change in the character of the bond between this particle and the surface. Thus, the interaction of the lattice excitons with the chemisorbed particles may cause a change in the relative content of the different forms of chemisorption and... 

More detailed investigations [38,39] have shown the kinetics of low-temperature electron transfer reaction (1) in bacteria to have a biphase character, i.e. to consist of two sections, one with a faster and the other with a slower decay of the Pf centres. Also, the type of kinetics of reaction (1) in bacteria at low temperatures has been found to depend on the conditions of sample preparation. The region of fast (t 50 ms) charge recombination at T < 230 K was observed only for the samples frozen in the dark. The extent of P decay was observed to decrease upon freezing the samples in the light. These results were explained by the presence of two channels for the decay of P+ centres by reactions with particles A and Q". The faster decay of P+ was assumed to be due to its reaction with A and the slower decay of P4 to its reaction with Q . The relative amounts of A and Q particles (i.e. the extent of electron transfer from the reduced form of the primary acceptor A to the secondary acceptor Q) was assumed to depend on temperature. This assumption explains why the character of P decay depends on whether P+ species are formed after or in the process of freezing the sample. 

Where the two phases are completely compatible, a homogeneous polyblend results which behaves like a plasticized resin (one phase). If two polymers are compatible, the mixture is transparent rather than opaque. If the two phases are incompatible, the product is usually opaque and rather friable. When the two phases are partially compatibilized at their interfaces, the polyblend system may then assume a hard, impact-resistant character. However, incompatible or partially compatible mixtures may be transparent if the individual components are transparent and if both components have nearly the same refractive indices. Furthermore, if the particle size of the dispersed phase is much less than the wavelength of visible light (requiring a particle size of 0.1/a or less), the blends may be transparent. 

The preservation of particle character and size throughout polymerization itself is very hard to determine. The size of the final polymer particles is easily determined by light scattering or microscopic methods since the dispersions can be diluted without changing the particle size. Measurements of the emulsion droplets in concentrated media on the other hand are a very difficult task and have already been discussed above. 

The statistical theories provide a relatively simple model of chemical reactions, as they bypass the complicated problem of detailed single-particle and quantum mechanical dynamics by introducing probabilistic assumptions. Their applicability is, however, connected with the collisional mechanism of the process in question, too. The statistical phase space theories, associated mostly with the work of Light (in Ref. 6) and Nikitin (see Ref. 17), contain the assumption of a long-lived complex formation and are thus best suited for the description of complex-mode processes. On the other hand, direct character of the process is an implicit dynamical assumption of the transition-state theory. 

The development of wave mechanics has been made possible through the introduction by de Broglie of a new principle dealing with the wave character of matter. The basis of this principle is the recognition that different interpretations are appropriate to different kinds of measurements thus atoms and electrons which have hitherto been regarded as discrete particles arc considered to possess a dual character, in the sense that they may possess both corpuscular and wave properties. A duality of a similar kind had been revealed earlier in studies on the propagation of light. 

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