Light, wave nature

Spectral lines are fiirther broadened by collisions. To a first approximation, collisions can be drought of as just reducing the lifetime of the excited state. For example, collisions of molecules will connnonly change the rotational state. That will reduce the lifetime of a given state. Even if die state is not changed, the collision will cause a phase shift in the light wave being absorbed or emitted and that will have a similar effect. The line shapes of collisionally broadened lines are similar to the natural line shape of equation (B1.1.20) with a lifetime related to the mean time between collisions. The details will depend on the nature of the intemrolecular forces. We will not pursue the subject fiirther here. 

If we think in terms of the particulate nature of light (wave-particle duality), the number of particles of light or other electi omagnetic radiation (photons) in a unit of frequency space constitutes a number density. The blackbody radiation curve in Fig. 1-1, a plot of radiation energy density p on the vertical axis as a function of frequency v on the horizontal axis, is essentially a plot of the number densities of light particles in small intervals of frequency space. 

The Schrodinger equation cannot be subjected to firm proof but was put forward as a postulate, based on the analogy between the wave nature of light and of the electron. The equation was justified by the remarkable successes of its applications. 

A hundred years ago it was generally supposed that all the properties of light could be explained in terms of its wave nature. A series of investigations carried out between 1900 and 1910 by Max Planck (1858-1947) (blackbody radiation) and Albert Einstein (1879-1955) (photoelectric effect) discredited that notion. Today we consider light to be generated as a stream of particles called photons, whose energy E is given by the equation... 

Ligand A molecule or anion bonded to the central metal in a complex ion, 409 characterization, 411-412 nomenclature, 648-649 Light, 159q absorption, 421 particle nature of, 135-136 wave nature of, 133-135 Limiting reactant The least abundant... 

The word radiant energy is the energy transmitted from one body to another in the form of radiations. This energy has wave nature and because it is associated with electric and magnetic fields, it is also called electro-magnetic radiations. The visible light, ultraviolet, infrared, X-rays, radio-waves and microwaves are all different forms of electromagnetic radiations. 

The second idea related to the LEED technique is, as its name indicates, the diffraction phenomenon. With the wave nature of the electrons established, information on the interaction of a beam of light with matter can be extrapolated to understand the interaction of a beam of electrons with a crystal. In this sense, the corresponding relationship is that of a monochromatic beam of light—that with a single frequency and single wavelength—with that of a beam of electrons of fixed energy. 

This section reviews the evidence for the wave nature of light and of X-rays, and then puts these two forms of radiation into the context of electromagnetic radiation in general. 

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