Energy electronic, deactivation mechanism

A very important bimolecular deactivation process is the electronic energy transfer (ET). In this process, a molecule initially excited by absorption of radiation, transfers its excitation energy by nonradiative mechanism to another molecule which is transparent to this particular wavelength. The second molecule, thus excited, can undergo various photophysical and photochemical processes according to its own characteristics. 

All Cl plasmas contain electrons with low energies, issued either directly from the filament but deactivated through collisions, or mostly from primary ionization reactions, which produce two low-energy electrons through the ionization reaction. The interaction of electrons with molecules leads to negative ion production by three different mechanisms [5] ... 

Photoscience covers a broad spectrum of interdisciplinary and interrelated subjects and it may be subdivided into photomedicine, photobiology, photochemistry and photophysics (Fig. 3-1). Photochemistry, in general, studies the reactions that occur through electronically excited states of molecules. Specifically, photochemistry studies the change of substance quality and characteristics by the influence of UV/VIS radiation. The mechanistic interpretation of the formation of photoproducts and their characterization and identification are typical domains of photochemistry. This research concept is strictly based on photophysics, which investigates the primary event of photon absorption by a molecule, the properties of electronically excited states and their deactivation mechanisms, such as for example fluorescence, phosphorescence and energy or electron transfer reactions, and non-... 

Figure 4 Orbital scheme illustrating the quenching of a photo-excited fluorophore FI by a nearby metal centre M via an electronic energy transfer (ET) mechanism. A simultaneous exchange of two electrons takes place, one from FI to M, one from M to FI. Following this circular electron motion, FI is deactivated. The excited M centre which is obtained can emit and relax to its ground state, but in most cases undergoes a non-radiative decay.

Thus, fluorescence quenching of 1 is to be associated to the complexation process and should be ascribed to the presence of the proximate Cu ion. The deactivation of the excited state of the anthracene subunit of 1 takes place either through an energy transfer mechanism or through an electron transfer mechanism. ... 

Although important from the point of view of the intrinsic stabihty of proteins upon UV irradiation, this issue has been only seldom addressed in gas phase experiments. Attention has been drawn to the field by pioneering excited-state calculations in the past decade conducted on peptides [177, 202-209], following an approach already successful for showing the role of Jto excited states in the deactivation of aromatic compounds, such as phenol or indole [210]. These authors emphasised the possible role of several excited states, namely a locally excited (LE) state and an intrabackbone charge transfer (CT) state to convert efficiently the photodeposited electronic energy into vibrational energy. The proposed deactivation mechanism involves a series of conical intersections (Cl), which enables sequential... 

Adsorbed layers, thin films of oxides, or other compounds present on the metal surface aggravate the pattern of deactivation of metastable atoms. The adsorption changes the surface energy structure. Besides, dense layers of adsorbate may hamper the approach of metastable atom sufficiently close to the metal to suppress thus the process of resonance ionization. An example can be work [130], in which a transition from a two- to one-electron mechanism during deactivation of He atoms is exemplified by the Co - Pd system (111). The experimental material on the interaction of metastable atoms with an adsorption-coated surface of... 

As well as returning to the ground state by radiative or radiationless processes, excited states can be deactivated by electronic energy transfer. The principal mechanisms for this involve dipole-dipole interactions (Forster mechanism) or exchange interactions (Dexter mechanism). The former can take place over large distances (5 nm in favourable cases) and is expected for cases where there is good overlap between the absorption spectrum of the acceptor and the emission spectrum of the donor and where there is no change in the spin... 

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