Electronic transitions, between quantized energy levels

Abstract Silver clusters, composed of only a few silver atoms, have remarkable optical properties based on electronic transitions between quantized energy levels. They have large absorption coefficients and fluorescence quantum yields, in common with conventional fluorescent markers. But importantly, silver clusters have an attractive set of features, including subnanometer size, nontoxicity and photostability, which makes them competitive as fluorescent markers compared with organic dye molecules and semiconductor quantum dots. In this chapter, we review the synthesis and properties of fluorescent silver clusters, and their application as bio-labels and molecular sensors. Silver clusters may have a bright future as luminescent probes for labeling and sensing applications. 

Unlike the processes of absorption and luminescence emission, scattering of light need not involve an electronic transition between quantized energy levels in atoms or molecules. Instead, a randomization in the... 

The model of metal-ammonia solutions that has emerged is based on ionization of the metal atoms to produce metal ions and electrons that are both solvated. The solvated electron is believed to reside in a cavity in ammonia, and thus it may behave as a particle in a three-dimensional box with quantized energy levels. Transitions between the energy levels may give rise to absorption of light and thereby cause the solutions to be colored. The dissolution process can be represented as... 

In contrast to ESR spectroscopy, which can only be used to study species with unpaired electrons, NMR spectroscopy is applicable to the investigation of all polymer samples. Nuclei with non-zero total nuclear spin (e.g., 1H, l3C, 19F, 14N) will have a magnetic moment which will interact with an external magnetic field resulting in quantized energy levels. Transitions between these energy levels form the basis of NMR spectroscopy. 1H and 13C... 

Quantum dots are objects with sizes in all three directions equal to few nanometers. Such systems resemble molecules and the energy levels of electrons in them quantize. Energies of the transitions between these levels depend on quantum dots material and size, and those transitions are the base for the quantum dots laser radiation. 

Where AE is the difference in energy between two quantized states, h is the Planck s constant and v is the frequency of the light. Then the molecule "absorbs" AE when it is excited from Pito E2 and "emits" AE when it reverts form 2 to The infrared absorption spectra originate in photons in the infrared region that are absorbed by transitions between two vibrational levels of the molecule in the electronic ground state. 

The Bohr model adds quantization to what is a classical mechanics description involving simple electrostatics. The Bohr model is certainly not a full quantum mechanical description of the atom. It assumes that the laws of classical mechanics do not apply during an electron transition between energy levels, but it does not state what laws should replace classical mechanics. 

Bohr postulated that a photon is emitted or absorbed only when the electron makes a transition from one energy level to another. The energy of an emitted or absorbed photon is equal to the difference between two quantized energies of the atom ... 

Bound electronic states exhibit a discrete spectrum of rovibrational eigenstates below the dissociation energy. The interaction between discrete levels of two bound electronic states may lead to perturbations in their rovibrational spectra and to nonradiative transitions between the two potentials. In the case of an intersystem crossing, this process is often followed by a radiative depletion. Above the dissociation energy and for unbound states, the energy is not quantized, that is, the spectrum is continuous. The coupling of a bound state to the vibrational continuum of another electronic state leads to predissociation. 

The energy absorbed or emitted by the molecules has only quantum fixed values—energy is quantized and is distributed on the energy levels corresponding to vibrational, rotational, or electronic levels. Electronic transitions occur between two molecular electronic levels. They are usually accompanied by rotational and vibrational transitions. 

Organic molecules are flexible structures. They rotate in solution, their bonds stretch, bend, and rotate, and they contain electrons that can move from one electronic energy level to another. We know from experimental observations and from theories of molecular structure that all energy changes within a molecule are quantized that is, they are subdivided into small, but well-defined, increments. For example, vibrations of bonds within molecules can undergo transitions only between allowed vibrational energy levels. 

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