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Light irradiation methods

EPR spectroscopy is usually used to calibrate the clock (i.e., to determine kc). The method described here uses EPR to detect the two radicals. These are the parent (R1 ) and the product (R2 ) of its reaction, be it cyclization, decarbonylation, decarboxylation, rearrangement, or whatever. The radical R1 is produced photochemi-cally in the desired inert solvent by steady and usually quite intense light irradiation of the EPR cavity. Typically, R1 and R2 attain steady-state concentrations of 10-8 to 10 6 M. [Pg.109]

The preparation of immobilized CdTe nanoparticles in the 30-60 nm size range on a Te-modified polycrystalline Au surface was reported recently by a method comprising combination of photocathodic stripping and precipitation [100], Visible light irradiation of the Te-modified Au surface generated Te species in situ, followed by interfacial reaction with added Cd " ions in a Na2S04 electrolyte. The resultant CdTe compound deposited as nanosized particles uniformly dispersed on the Au substrate surface. [Pg.178]

Thus, silver nanoparticles grow gradually during UV light irradiation (processes al-a3 in Figure 2). Nanoparticles of other noble metals such as gold, copper, platinum, and palladium can also be deposited by this method. [Pg.263]

The term nonlinear optical property refers to an optical property, which can be modified by exposing the material to intense light irradiation. In this section, we focus on the cascaded first- (/ 1 ) and third-order ( / ) susceptibilities describing nonlinear absorption (ESA and 2PA) and nonlinear refraction (n2) processes. Z-scan, pump-probe, and two-photon upconverted fluorescence techniques are among the most used experimental methods for determining optical nonlinearities. [Pg.119]

A spectrophotometer which allows spectroscopic and kinetic measurements to be made on a light irradiated sample has been developed by Ranalder et al. 5). The instrument is completely controlled by a small PDP-8/I computer. Great flexibility is introduced through software control. Several data collection routines have been written, and methods for determining molar absorption coefficients of metastable states have been discussed. [Pg.27]

This similar methods involves UV light irradiation, with light intensity, stirring speed, suspension volume and temperature influencing particle growth. Fig. 6.5. Shorter irradiation times can be used to limit the amount of particle deposition. Photo-deposited samples do not require calcination hence there is little chance of particle agglomeration. [Pg.379]

The incorporation of a cationic azobenzene derivative, p-( a> -dimethyl-ethanolammonioethoxyj-azobenzene bromide, into nanoporous silica films and the photochemical reactions of the adsorbed dye were investigated. The nanoporous silica films were prepared from tetramethoxysilane and octadecyltrimethyl-ammonium chloride by the rapid solvent evaporation method which we have reported previously. The adsorption of the cationic azo dye was conducted by casting an ethanol solution of the dye onto the nanoporous silica films. Upon UV light irradiation, trans-azobenzene isomerized photochemically to the c/s-form and photochemically formed c/ s-form turned back to the frans-form upon visible light irradiation. The nanoporous silica films were proved to be an excellent reaction media to immobilize organic photocromic species. [Pg.865]

Scientific research has led to significant success in the practical applications of organic ion radicals. Such applications should widen in the future. It is very important to concentrate effort on the elaboration of preparative methods of ion radical organic chemistry, including stereospecific methods. The correct choice of new developmental procedures opens up a wealth of new directions. It is hoped that interest in this area will continue to ensure the flow of new ideas and reactions, particularly in the area of organic synthesis in liquid phase and without light irradiation. [Pg.417]

The mechanism of aminyl radical generation from PTOC carbamates follows closely the radical chain mechanism of alkyl radical generation from PTOC esters. The chain reaction sequence involves the series of steps shown in Scheme 8. Several methods for inducing N —O bond cleavage are possible. Photochemical decomposition of 29 via visible light irradiation is used to initiate the chain reaction sequence at ambient or subambient temperature reactions have been run as low as -78°C (91TL6493). [Pg.12]


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