Charge-transfer process spectrum

The shallow and deep levels play the important role in the sensitization process. Detailed research in this field has shown the presence of four local electron centers in the energetic spectrum of the sensitized PVC in the range 0.6-3.3 eV [63,64]. The density of localized states was of the order 1018 1019 cm-3. These can play essential role in spectral and chemical sensitization due to their influence on photogeneration, recombination and charge transfer processes. 

In n-hexane, a similar band with a maximum at around 384 nm was observed with a comparably fast risetime, so that one can conclude that the photoinduced charge-transfer process in this fluorinated derivative is a quasi-barrierless process in both polar and non-polar solvents. Preliminary DFT calculations indicate that in vacuum DMABN-F4 is nonplanar in the ground state in contrast to DMABN [7]. The fact that the observed CT state absorption spectrum is blue-shifted compared to that of DMABN and of the benzonitrile anion radical (Fig. 3) might be an indication that the equilibrium geometry of the CT state of DMABN-F4 is different from that of the TICT state of DMABN or might be due to the influence of the four fluorine atoms. 

From a practical standpoint, much of the interest in the role of excited states in ionic interactions stems from their importance in ionospheric chemistry.Ih In addition, it has been realized more recently that certain ion-neutral interactions offer a comparatively easy means of populating electronically excited reaction products, which can produce chemiluminescence in the visible or UV region of the spectrum. Such systems are potential candidates for practical laser devices. Several charge-transfer processes have already been utilized in such devices, notably He+(I,He)I + and He2+(N2,2He)N2+.3 Interest in this field has stimulated new emphasis on fundamental studies of luminescence from ion-neutral interactions. 

The electronic transitions of silicalite and TS-1 in the UV-visible spectrum have provided significant information about the structure of TS-1. The diffuse reflectance spectra of the two materials (Fig. 11) show a strong transition at 48,000 cm-1 that is present in the spectrum of TS-1 and absent from that of silicalite. This transition must be associated with a charge-transfer process localized on Tiiv. The frequency of this transition is modified by the presence of H20 (Fig. 12). As the H20 partial pressure increases, the peak at 48,000 cm- is progressively eroded with formation of a lower-frequency absorption, which reaches a new stable maximum value at 42,000 cm. These frequencies come very close to those that can be calculated by the Jorgensen equation for Tiiv tetrahedrally and octahedrally coordinated to oxygen, respectively. Furthermore,... 

A semi-quantitative description of the core level spectrum and the charge-transfer process can be obtained from a simple two-level MOLCAO-model based on the sudden approximation 155 157,160). Here, we follow the formulation of Larsson157) and consider the influence of a core hole on a single electron in an MO formed by linear combination of AO s Ul and uM centred on the ligands (L) and the central metal ion (M). In the ground state, before ionization, the electron is in a bonding orbital... 

There are many other Prussian blue analogs for which the visible spectrum is complex and not understood. Heavy metal ferricyanides and hexacyano complexes of other transition metals with less than d configurations are in this class due to the presence of ligand-metal charge transfer processes. 

Figure 19 shows the typical photoluminescencc spectrum of the anchored vanadium oxide catalyst prepared by photo-CVD methods (a), its corresponding excitation spectrum (b), and the UV absorption spectrum of the catalyst (c) (56,115,116). These absorption and photoluminescence spectra (phosphorescence) are attributed to the following charge-transfer processes on the surface vanadyl group (V=0) of the tetrahedrally coordinated VO4 species involving an electron transfer from to V and a reverse radia-... 

As shown in Fig. 65, titanium-silicon binary oxides prepared by the sol-gel method exhibit a characteristic photoluminescence spectrum near 480 nm upon excitation at 280 nm. The absorption and photoluminescence spectra are attributed to the charge-transfer processes on the highly dispersed tetrahedral titanium oxide species embedded in the Si02 matrices (168, 200, 201). When the titanium content of the oxides was decreased, the intensity of the photoluminescence spectrum increased, and its peak wavelength shifted to shorter wavelengths. 

Meaningful ESR or spectral data have not been obtained. Only a band at 29800 cm. , with a shoulder at 27800 cm. can be resolved in the reflectance spectrum of the black compound in KI the energy and intensity both suggest these arise from charge transfer processes. 

Fluorescence and Chemiluminescence Spectroscopy. - The fluorescence excitation spectrum of PF3 at 9-13 eV, using monochromatised synchrotron radiation, has been examined to resolve the pyramidal geometry of the X Ai ground state of the PFs" cation, which was also confirmed by ab initio calculations. Dimethylamino-substituted triphenylphosphines exhibit dual fluorescence in polar solvents, and fluorescence-decay measurements have shown that the photo-induced intramolecular charge-transfer process occurs in a few picoseconds, even in weakly-polar solvents. 

Mo-MCM-41 (1.0 Mo wt%) exhibits a photoluminescence spectrum at around 400-600 nm upon excitation at around 295 nm (defined as X), which coincides with the photoluminescence spectrum of the tetrahedrally coordinated Mo-oxides hi ly dispersed on Si02, as shown in Fig. 1 [11]. The excitation and emission spectra are attributed to the following charge transfer processes on the Mo-0 moieties of the tetrahedral molybdate ions (MoO, ), involving an electron transfer from the O to Mo ions and a reverse radiative decay from the charge transfer excited triplet state [2,11]. 

Figure 7. Molecular orbital energy-level diagram developed by Bramanti et al. (118) for thallium sites in T1(I) doped KCl both intraatomic and Cl—Tl charge-transfer processes are involved in the transitions observed in the absorption spectrum. [Adapted from reference (118).]...

The ruthenium oligothienylacetylide complexes 93 (Chart 5.30) [106] and the oligothienylferrocene complexes 94a and b were electrochemically polymerized [107]. The voltammetry of poly-94a and poly-94b films contains redox waves due to both the ferrocene and backbone redox couples. Low-energy absorption bands appear upon oxidation of both the Fe centers and the conjugated backbone in the UV-Vis-near-IR spectrum of the films, and these have been attributed to charge-transfer processes. The poor solubility of 94b prevents electropolymerization at room temperature however, polymer films can be prepared at elevated temperatures. Electropolymerization of 95, in which hexyl chains have been added to increase the monomer solubility, has also been reported [108]. 

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