Energy of light quanta

The bond dissociation energies of various bonds are tabulated in Table 1 and energies of light quanta are shown in Table 2. It is apparent that the bond energies of the C—C, C—H and C—O bonds are in the... 

The fact that chemical change can be induced by visible light shows that the energy of electronic activation can under appropriate circumstances find its way to the critical position in the molecule, but from what has been said it should be clear that no direct connexion exists between the magnitude of light quanta and their possible chemical effects. This statement is borne out by all the facts of photochemistry. 

In 1958, Franz [45] and Keldysh [46] independently theoretically predicted the absorption by a semiconductor, placed in an electric field, of light quanta which have an energy less than the width of the forbidden gap. The effect is connected with interband tunneling (Fig. 20). The valence band electron tunnels from point xl to point 3c, then it absorbs a quantum with a frequency lo < Eg (Eg is the width of the forbidden gap) and further tunnels to point x2. Using the law of conservation of energy and the law of conservation of imaginary momentum (see the previous section), it is easy to show that light absorption at point 3c, which lies exactly between points acj and x2, is optimal. Consequently... 

Luminescence is defined as emission of light by materials in the visible, UV, and IR spectral range after input of energy [2], Emission of light quanta by molecules from a (photo) excited state proceeds via transition of an electron to a lower energy level. Depending upon the way in which the excited state is generated, a distinction is made between photoluminescence, chemoluminescence, radioluminescence, and thermoluminescence (Table 5.1). In the case of photo-... 

The energy of light is emitted, absorbed, or converted to other forms of energy in individual units referred to as quanta (singular quantum). The unit of light energy is often referred to as the particle of light called the photon. 

The key step of the process is the water splitting under absorption of light quanta of relative low energy. Here we will focus mainly on the latter process which appears to be one of the most enigmatic reactions in chemistry and photochemistry and will only briefly consider the light energy conversion reaction centers of PS I and PS II. 

Infrared spectra are usually recorded by measuring the transmittance of light quanta with a continuous distribution of the sample. The frequencies of the absorption bands Us are proportional to the energy difference between the vibrational ground and excited states (Fig. 2.3-1). The absorption bands due to the vibrational transitions are found in the... 

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