Static spectral sensitization

Models for the static spectral sensitization of coordination compounds are discussed. Among them, ion pairs with oppositely charged metal complexes, where intervalence charge-transfer interactions occur, appear to be promising exarrples. The spectra and the electron transfer kinetics,of mixed-valence ion pairs of ihe type M /fMCNjgJ4-, where M + = Fe3 Cu2 UO V02 are discussed in detail. 

Static spectral sensitization. To overcome some of the disadvan-tages of the dynamic sensitization, the concept of static sensiti-... 

The advantages in applying mixed-valence compounds are due to the fact that the energy of the IT transition may be varied by convenient synthetic procedures, in addition, the photochemical behavior may be predicted using the theoretical treatment proposed by Hush. However, the most serious restriction for the application of mixed-valence compoun ds in the static spectral sensitization arises from the fast back electron transfer. Therefore, very efficient scavenging reactions are required in order to suppress back electron transfer. 

Gratzel, M. (Editor). 1983. Energy Resources through Photochemistry and Catalysis (Academic Press, New York). Hennig, H. and Rehorek, D. 1986. Static spectral sensitization of photocatalytic systems. In A.B.P.Lever (Ed.), Excited States and Reactive Intermediates, ACS Symposium Series, 307. 104-119. 

Static SIMS has been demonstrated to be a valuable tool in the chemical characterization of surfaces. It is unique in its ability to provide chemical information with high surface sensitivity. The technique is capable of providing mass spectral data (both positive and negative spectrometry), as well as chemical mapping, thereby giving a complete microchemical analysis. The type of information provided by... 

Almost all of this work has been conducted using powdered samples. Single crystal samples could have some advantages. They would yield absolute orientational information, provide increased sensitivity and resolution as compared to static powders, and allow more confident spectral assignment, particularly for minor components. Difficulty in preparing single crystals of suitable size (several hundred milligrams would be desirable) is a major obstacle to this type of study. 

We have presented two types of nonlinear IR spectroscopic techniques sensitive to the structure and dynamics of peptides and proteins. While the 2D-IR spectra described in this section have been interpreted in terms of the static structure of the peptide, the first approach (i.e., the stimulated photon echo experiments of test molecules bound to enzymes) is less direct in that it measures the influence of the fluctuating surroundings (i.e., the peptide) on the vibrational frequency of a test molecule, rather than the fluctuations of the peptide backbone itself. Ultimately, one would like to combine both concepts and measure spectral diffusion processes of the amide I band directly. Since it is the geometry of the peptide groups with respect to each other that is responsible for the formation of the amide I excitation band, its spectral diffusion is directly related to structural fluctuations of the peptide backbone itself. A first step to measuring the structural dynamics of the peptide backbone is to measure stimulated photon echoes experiments on the amide I band (51). 

High mass-spectral resolution is often essential in structural work as the answers obtained with conventional low-resolution instruments may not always be unequivocal in terms of atomic composition in the studied molecules. While the resolution obtained in a GC/MS model on the individual chromatographic peaks is short of the typical values obtained under static conditions, it is frequently sufficient to yield the exact molecular weights. Due to the design features of double-focusing instruments, sensitivities are typically lower than those obtained with the conventional GC/MS instruments. 

Field desorption (FD) and fast atom bombardment (FAB) mass spectrometry provides mass spectral information about compotmds that are not very volatile but these two techniques are not used often in polymer science since they have several disadvantages. Electrospray ionization (ESI) mass spectrometry can also be used to obtain the above information about polymers, but ESI spectra are generally complicated due to differences in charge state distributions. Static secondary ion mass spectrometry (static SIMS) is a surface-sensitive MS technique, which is suitable for studying the interfaces of polymers with respect to chemical structure and molecular weight as well as end groups and surface contaminants. Laser desorption... 

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