Continuous irradiation

Bromination of sulfolane by BrCl under uv irradiation gives 2-bromosulfolane [29325-66 ] which reacts further to give i7j -2,5-dibroniosulfolane [30186-52-8] (5). Continued irradiation converts the <7j -isomer to /n j -2,5-dibroniosulfolane [30186-54-0] which yields first the trans-2 4 isomer [30186-53-9] and then the trans-2 4 isomer [15091 -30-2] upon further irradiation. 

The cryophotoaggregation phenomenon was first observed for Ag atoms 112) entrapped in Ar at 10-12 K (see Fig. 14). The trick essentially involves narrow-band, continuous irradiation into the... 

Fig. 19. The optical spectrum of the products of a Ag Kr — 1 10 cocondensation reaction, (A) after deposition at 10-12 K, and (B) after 60-min, narrow-band (8 nm), 325-nin continuous irradiation from an Oriel 500-W xenon lamp-Schoeffel monochromator assembly (152).

Velapoldl et al. (64) used a similar approach but prepared fibers of uniform diameter (5-45 pm) from Inorganic Ion-doped glasses. The fluorescence parameters of these materials can be changed by substituting various Ions, such as Tb , Sm , Eu , Mn, UOj, Cu, and Sn. They show excellent stability under Irradiation using Incident excitation (measurement Imprecision of 1% under continuous Irradiation In the microscope for 24 h) and have a fluorescence flux density proportional to the fiber length. 

We have also tried the trapping reactor system, in which ammonia is trapped on the catalyst/adsorbent and microwave is irradiated intermittently. However, due to the small specific surface area and the small ammonia adsorption capacity on the employed CuO, the trapping system was not effective compared to the continuous irradiation. Further study should be made to develop a material having high ammonia adsorption capacity and high efficiency for microwave absorption. Supported CuO on high surface area material or preparation of high surface area CuO can be effective. 

Varret F, Boukheddaden K, Codjovi E, Enachescu C, Linares J (2004) On the Competition Between Relaxation and Photoexcitations in Spin Crossover Solids under Continuous Irradiation. 234 199-229 Varret F, see Bousseksou A (2004) 235 65-84 Varret F, see Tuchagues J-P (2004) 235 85-103... 

Catalysis and Synthesis in the Laboratory. Research on the practical applications of catalysis was not matched in the laboratory. We began a study of metal and non-metal catalyzed reactions early in our sonochemistry program. Our first project was to develop a convenient method of hydrogenating a wide range of olefins. We chose formic acid as our hydrogen source and found it to be effective. For example, with continuous irradiation, palladium catalyzed hydrogenations of olefins are complete in one hour(44). 

Recently we found that freshly prepared nickel powder is an efficient hydrosilation catalyst when continuously irradiated(49). 

The effects of soil depth and moisture on pesticide photolysis were studied. Moist soil at depth of 3, 2.5, 2, 1.5, 1, and 0.5 mm were each dosed at 2.5 pg/g with 14C-niclosamide and photolyzed under a xenon lamp at constant temperature. Samples were removed after 20, 40, 110, and 153 h of continuous irradiation. The decrease in percent of niclosamide and the appearance of degradates were followed by analyzing the soil extracts by HPLC [76],... 

There is better control of the progress of a reaction obtained by interrupted, pulsed, or continuous irradiation. 

An 88% yield of the product was obtained by applying 15 x 1 min pulses of irradiation. No rationalization for the increased yields obtained in these pulsed versus continuous irradiation experiments can be given at present (see also Scheme 2.6). 

Microwave heating has also been employed for performing retro-Diels-Alder cycloaddition reactions, as exemplified in Scheme 6.94. In the context of preparing optically pure cross-conjugated cydopentadienones as precursors to arachidonic acid derivatives, Evans, Eddolls, and coworkers performed microwave-mediated Lewis acid-catalyzed retro-Diels-Alder reactions of suitable exo-cyclic enone building blocks [193, 194], The microwave-mediated transformations were performed in dichloromethane at 60-100 °C with 0.5 equivalents of methylaluminum dichloride as catalyst and 5 equivalents of maleic anhydride as cyclopentadiene trap. In most cases, the reaction was stopped after 30 min since continued irradiation eroded the product yields. The use of short bursts of microwave irradiation minimized doublebond isomerization. 

Irradiation of the photosensitizer solution takes place in a vessel (1) by means of a lamp (2). During measurements, a continuously irradiated solution is transferred with a peristaltic pump (5) from the vessel (1) into the measuring cell (6) of a chemiluminometer (7). Control of the unit, signal recording, and data processing are performed by a computer (8). The tube (4) serves for injection of various components during measurement. 

One of the possible reasons of the drop of the initiation rate could lie in the fast consumption of the photoinitiator. With a phosphine oxide photoinitiator (LucirinTPO), as much as 75% of this compound was destroyed within 0.2 s of UV exposure at a light intensity of 400 mW cm 2 (Figure 7). When the light was cut off at that time (rj=0), the polymerization was found to continue to proceed nearly as fast as upon continuous irradiation. The fact that the polymerization is only slightly faster upon continuous irradiation than in the dark suggests that rj has already dropped to a low value when (Rp)max is being measured, at 20% conversion. The important post-polymerization, which lasts only a few seconds, is due to the high concentration of macroradicals that continue to polymerize in the dark. 

On the Competition Between Relaxation and Photoexcitations in Spin Crossover Solids under Continuous Irradiation... 

Several other light-induced phenomena associated with spin transition systems have recently been reported. These include light induced thermal hysteresis (LITH), which is another example of light induced bistability, discovered for the SCO compound [Fe(PMBiA)2(NCS)2] which undergoes a very abrupt thermal ST around 170 K with hysteresis [174]. Irradiation of the sample at 10 Kwith green light resulted in the population of the LIESST state. When the temperature was raised to 100 K and lowered back to 10 K under continuous irradiation a wide thermal hysteresis loop resulted. The... 

The sample is continuously irradiated and the fluctuations in the fluorescence intensity arise due to any event which makes the fluorophore unavailable to be excited to the emissive singlet excited state, such as diffusion of the fluorophore out of the detection volume, formation of a dark state, such as a triplet excited state, or photoreaction. The concentration of fluorophore in the detection volume has to be low (10 13—10 8M) so that the fluctuation in the intensity for one molecule is observable over any background emission. The high concentration limit is a consequence of the fact that the correlated photons from single molecules scale with the number of molecules in the detection volume, while the contribution from uncorrelated photons, arising from the emission from different molecules, scales with the square of the number of molecules. The lowest concentration is determined by the probability of finding a molecule in the detection volume.58... 

Optical properties of dendrimers bearing eight chromophores have been examined by single molecule spectroscopy techniques. It is especially exciting that variations in the spectra are recorded if one of these dendrimers is observed for a period of time under continuous irradiation.1481 The fluorescence intensity of the dendrimer nanoparticle also jumps between discrete emissive levels. All these findings suggest the existence of strong electronic interactions between several perylene imide chromophores within one dendrimer and provide new... 

The charge-transfer salts of carbonylmetallates are thus distinguished from the iodide salts in the breadth of photochemistry that obtains upon exposure to visible light. For example, the continuous irradiation of the... 

In heterogeneous photoredox systems also a surface complex may act as the chromophore. This means that in this case not a bimolecular but a unimolecular photoredox reaction takes place, since electron transfer occurs within the lightabsorbing species, i.e. through a ligand-to-metal charge-transfer transition within the surface complex. This has been suggested for instance for the photochemical reductive dissolution of iron(III)(hydr)oxides (Waite and Morel, 1984 Siffert and Sulzberger, 1991). For continuous irradiation the quantum yield is then ... 

The combination of the photocatalytic production and the photocatalytic degradation will result in a steady-state concentration of H202 during continuous irradiation. Steady-state concentrations of H202 in excess of 100 pM were obtained in illumi-... 

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