Irradiation Experiments

The use of high-power lasers with short wavelengths allows generation of the most extreme shock pressures in laboratories [15], but only in conjunction with extremely short pulse durations in the nanoseconds range. Laser irradiation shock experiments may be regarded as adequate simulations of hypervelocity impacts of microgram-mass micrometeorites onto atmosphere-free bodies such as the Moon [21] as well as onto spacecraft. Such impacts do not occur on Earth, as high-speed micrometeorites bum up in the atmosphere. 

Pioneering experiments in the 1960s demonstrated the possibility of accelerating thin foils to velocities up to several kilometers per second by the blast from an electrically exploded thin metallic foil [26-28]. The principle of such a tool — an electrical discharge gun that has been developed at the Laboratoire de Combustion et de Detonique in Poitiers (France)—is shown in Fig. 1.4. The sudden discharge of a low-inductance RLC circuit into a well-designed foil of thin aluminum, acting as a fuse in the circuit, turns this fuse into a plasma. The 

Regarding the pressure duration, the electrical discharge technique forms a bridge between laser (-nanoseconds) and high-explosive (-microseconds) shock experiments. Our electrical discharge device produces shock waves that last between -10 and 100 ns (Fig. 1.1). The shorter time limit is valid for the highest pressure and reflects the need to use thinner projectiles to achieve the higher flyer-plate velocities. 

The high-explosive setups used at the Emst-Mach-Institut, Fraunhofer-Imtitut fur Kurzzeitdynamik in Efringen-Kirchen, Germany, are basically composed of two parts with different experimental functions a shock generating and a recovery system (Fig. 1.6 [3,29,30]). The shock-generating system consists of a 

The advantage of the high-explosive assembly over laser irradiation and electrical discharge devices is the controlled recovery of the sample. The recovery system consists of two rectangular steel blocks acting as momentum traps and a cylindrical ARMCO iron container, which is embedded into the upper steel block. The disc-shaped specimen is encapsulated in this container. This design allows complete recovery of relatively large samples (diameters of 10-20 mm and thickness up to several millimeters). 

The photochemical behaviour of both isomers of 1 was smdied in acetonitrile solutions. The electronic absorption spectra of the isomers are shown in Fig 4.11 la exhibits only one absorption band with maximum at 313 nm with a shoulder at about 255 nm and no absorption in the visible, while the spectrum of lb shows a band with maximum at 329 nm, a shoulder at 376 nm and a second broad band with maximum at 600 nm. The absorbance in the visible is a very useM tool for monitoring both the photoeoloring (ring-closure, la lb) and photobleaching (ring-opening, lb la) reactions. 

The quantum yields were evaluated by measuring the absorbance changes at 600 mn, i.e., the production (reaction la lb) or the disappearance (reaction lb - la) of lb and by using an equation analogous to (4.12). Unfortunately, the UV light used to cause the photoreaction of la is partially absorbed by the product lb (see Fig. 4.11), so that the quantum yield progressively decreases with the 

549 Medium pressure Hg, 125 W Interference, 18 nm Reinecke s salt Aberchrome 540 

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The Omega West Reactor (OWR) is a water-cooled pool reactor operated by for the DOE by Los Alamos National Laboratory (LANL) for neutron irradiation experiments at a power of 8 MWt... 

Small scale test runs prior to preparative irradiation experiments may be carried out in tubes which are either taped to the lamp housings (immersion wells) depicted in Figures 13-1 and 13-2 or placed in turntable reactors ( merry-go-rounds ). These arrangements permit the simultaneous irradiation of several samples, but only a fraction of the available light emission is used. In Figure 13-4 a simple reactor is shown which focusses almost all the emitted light into one sample which can be scaled up also to semi-preparative volumes. In this way the necessary irradiation time can be reduced sharply. 

P -Bonding is obviously also the initiating step in the complex photoisomerization sequence of the stereoisomeric 1,5-dien-3-ones (162) and (163) in ethanol. After low conversions of the starting dienones, an isomer containing an analogous chromophoric system [(164) and (165), respectively] was found to build up temporarily in each case. On longer photolysis times, both compound pairs (162)/(164) and (163)/(165), are consumed, and the mixtures of the four diastereomers (166)-(169) were isolated from both runs. According to separate irradiation experiments with each of these products, (166) and (167) on one hand, and (168) and (169) on the other, are... 

Irradiation of UDMH-NO-Air Mixtures. One experiment was performed in which approximately equimolar amounts of NO and UDMH were irradiated for 2.5 hours. The reactant and product concentrations are summarized in Table II and are shown graphically for selected species in Figure 3. The UDMH-NO irradiation experiment can be considered to have three stages as summarized below ... 

Figure 10.7 The phase diagram (a) and the glass transition temperatures (b) of a PSC/PVME mixture obtained, respectively, by light scattering and differential scanning calorimetry (DSC). Irradiation experiments were performed in the miscible region at 127 C indicated by (X) in the figure of trans-cinnamic acid-labeled polystyrene/poly(vinyl methyl ether) blends.

Ishino, S., Nakanishi, H., Norisuye, T., Awatsuji, Y. and Tran-Cong-Miyata, Q. (2006) Designing a polymer blend with phase separation tunable by visible light for computer-assisted irradiation experiments. Macromol. Rapid. Commun., 27, 758-762. 

Scheme 5b, solutions (pH=7.5) of these DNA strands were subsequently irradiated under anaerobic conditions, after reduction of the flavin with sodium dithionite [51]. HPLC analysis of samples removed from the assay solution during such an irradiation experiment showed clean transformation of the Tf=T-containing DNA strands into the repaired TfT-containing DNA strands (Fig. 2). These experiments showed for the first time that a reduced flavin, if incorporated into DNA, can inject an extra electron into a DNA du-...

Figure 3 shows an ion exchange HPLC analysis of the irradiation experiment performed with the duplex 13. The starting duplex 13 elutes at a retention time of 13 min. The cleaved DNA strand has a retention time of 11 min. Clearly evident again is the clean conversion of the unrepaired duplex 13 into the cleaved, repaired , DNA fragment. 

The construction of a custom-built parallel reactor with expandable reaction vessels that accommodate the pressure build-up during a microwave irradiation experiment has also been reported [88]. The system was used for the parallel synthesis of a 24-member library of substituted 4-sulfanyl-lH-imidazoles [88]. 

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). 

Other microwave-assisted SPOS processes reported in the literature are summarized in Scheme 12.8. The addition of isocyanates to amines bound to Wang resin, for example, was studied both under conventional conditions at room temperature and under the action of microwave irradiation in open vessels by use of a monomode instrument. By monitoring the progress of the addition by on-bead FTIR it was demonstrated that the microwave procedure proceeded significantly faster than the reaction at room temperature (12 compared with 210 min) [38], The temperature during the microwave irradiation experiment was not determined, however, so it is unclear if any nonthermal microwave effects were responsible for the observed rate-enhancements (Scheme 12.8a) [38]. 

Direct irradiation or thermolysis of a diazo-compound (2) is believed to generate the carbene initially in its singlet spin state. Triplet sensitization (5) is presumed to give the triplet carbene directly without first forming its singlet state via the triplet diazo-compound. In some cases, careful comparison of the results of direct irradiation experiments with those from triplet sensitization can provide useful information to identify the spin state initiating a reaction. 

Irradiation of DMDAF in benzene solution at room temperature generates a transient intermediate that appears within the rise-time of the laser and decays by a pseudo first-order kinetic path with a half-life of 51 ns. The optical spectrum of the intermediate is essentially the same as that observed in the low temperature irradiation experiment. 

S. Coussan, M. E. Alikhani, J. P. Perchard, and W. Q. Zheng, Infrared induced isomerization of ethanol dimers trapped in argon and nitrogen matrices Monochromatic irradiation experiments and DFT calculations. J. Phys. Chem. A 104, 5475 5483 (2000). 

In the above expressions, the subscript F refers to the full relaxation and exchange matrices that include the P2 and P2 protons since their magnetizations do not experience rf saturation during in the on-resonance saturation experiment and during ti + t in the off-resonance irradiation experiment (control spectrum). Hence, experience coupled recovery with the rest of the protons during these periods. The subscript r refers to the reduced matrix containing elements for I, I, PI, and PI extracted from the full matrix. We have implemented the above expressions as an option in the CORCEMA-ST program. 

Jang and McDow (1997) studied the photodegradation of benzo[a]anthracene in the presence of three common constituents of atmospheric aerosols reported to accelerate benzo [a] anthracene, namely 9,10-anthroquinone, 9-xanthone, and vanillin. The photo-degradation experiments were conducted using a photochemical reactor equipped with a 450-W medium pressure mercury arc lamp and a water bath to maintain the solution temperature at 16 °C. The concentration of benzo [a] anthracene and co-solutes was 10" M. Irradiation experiments were conducted in toluene, benzene, and benzene-c/e- Products identified by GC/MS, FTIR, and NMR included benzo[a]an-thracene-7,12-dione, phthalic acid, phthalic anhydride, 1,2-benzenedicarboxaldehyde, naphtha-lene-2,3-dicarboxylic acid/anhydride, 7,12-dihydrobenzo[a]anthracene, 10-benzyl-10-hydroan-thracen-9-one, benzyl alcohol, and 1,2-diphenylethanol. 

An apparent decrease in the emission quantum yield and/or distortion of the band shape due to the reabsorption of emitted radiation. If such an effect is not corrected or compensated for, results of an emission experiment may prove to be incorrect. This is especially true in fluorescence quenching experiments conducted to evaluate the stoichiometry and affinity of ligand binding. 2. In a light irradiation experiment, the absorption of incident radiation by a species or molecular entity other than the intended primary absorber. See Fluorescence... 

Figure 3 Absorption spectrum of the DNA film around the K-shell absorption edge of phosphorus [18]. Dotted line is the total photoelectron yield of KH2PO4. Three vertical arrows indicate the X-ray energies used for the irradiation experiments shown in Fig. 4.

Direct irradiation of 130a-c and 130f led to modest yields of 136a-c and 136f. The yields of the amine could be reduced by the addition of the triplet quencher TMDD. Triplet sensitized photolysis led to increased yields of the amine, even in cases in which the reduction product was not found in direct irradiation experiments. " Triplet sensitized photolysis always led to some of the singlet products 132,133, and/or 134. ... 

The sharp increase in adsorbance which is observed near 256 and 340 nm is characteristic of the o-rearranged product. Similar results are also obtained when the irradiation experiments are carried out under nitrogen atmosphere, indicating that the photo-oxidation reported by Hiraoka and Pacansky (23) for poly(p-hydroxystyrene) is not a factor in this instance. 

This work was supported by a research assistantship (to DTA) from Sheffield City Polytechnic and was carried out in collaboration with Dow Corning Ltd., Barry and Central Electricity Generating Board, Bristol. Irradiation experiments were performed at Berkeley Nuclear Laboratories. 

In a lecture presented to the Faraday Society,332 Norrish commented on why the higher vibrational levels of NO were observed in the nitrosyl halide experiments but not by absorption in NO irradiation experiments. He reasoned that, as the emission of NO from the AZH + state populates the first five vibrational levels of NO almost equally,341 the fast-exchange reaction (4) can quickly eliminate all the vibrational levels above the first. However, in the nitrosyl halide experiments, the NO may be formed preferentially in very high levels, such as v — 10 or 11, almost exclusively. Thus, reaction (4) cannot occur initially, and depopulation must be by reaction (2). Reaction (2) is considerably slower than reaction (4), because of the increased difference in vibrational energy between the reactants and products resulting from an-harmonic effects. 

Diffusion phenomena, as well as calculations of diffusion entropy and enthalpy, have been successfully explained by ascribing multiple ionization levels to vacancies that are the same as those observed for the vacancy in low-temperature irradiation experiments (14-16). Vacancies and self-interstitials are interchangeable as far as diffusion is concerned, provided that both have charge states. 

It must be remembered that irradiation experiments can be performed with monophasic systems (in the absence of an aqueous phase) or in extraction conditions in the presence of an aqueous phase, in static or dynamic conditions (organic and aqueous phases continuously stirred with a dedicated stirrer unit (20), magnetic stirrer, or sparging with air). 

This experiment is of particular importance in that it points the way to a new method of investigating photolyses in solution. As a method of preparing new radicals for structural studies it probably has less application than the difficult but extremely effective irradiation experiments of Fessenden and Schuler (1960 Fessenden, 1961). These workers passed a beam of high-energy electrons through one of the pole pieces of the electromagnet into liquid ethane in the resonant cavity. In this manner a standing concentration of ethyl radicals was obtained which was quite sufficient not only for detection but for... 

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