Initiation by flash

Electronic excitation from atom-transfer reactions appears to be relatively uncommon, with most such reactions producing chemiluminescence from vibrationaHy excited ground states (188—191). Examples include reactions of oxygen atoms with carbon disulfide (190), acetylene (191), or methylene (190), all of which produce emission from vibrationaHy excited carbon monoxide. When such reactions are carried out at very low pressure (13 mPa (lO " torr)), energy transfer is diminished, as with molecular beam experiments, so that the distribution of vibrational and rotational energies in the products can be discerned (189). Laser emission at 5 p.m has been obtained from the reaction of methylene and oxygen initiated by flash photolysis of a mixture of SO2, 2 2 6 (1 )-... 

It is appropriate to mention here an alternative method for synthesizing monodispersed polymers which was developed by Zimm.67 Emulsion polymerization is initiated by flash photolysis. The second flash terminates the polymers initiated by the first one, starting on a new chain to be terminated by the third flash, and... 

In oriented, partially dehydrated multilayers, under conditions suitable for X-ray diffraction studies, the sarcoplasmic reticulum vesicles retain much of their ATP energized Ca transport activity [200-202], The Ca transport can be initiated by flash-photolysis of P -l(2-nitro)phenyl-ethyladenosine-5 -triphosphate, caged ATP [203-208], The flash-photolysis of caged ATP rapidly releases ATP and effectively synchronizes the Ca transport cycle of the ensemble of Ca -ATPase molecules [190-192,201,209],... 

Horikawa Y, Goel A, Somlyo AP, Somlyo AV 1998 Mitochondrial calcium in relaxed and tetanized myocardium. Biophys J 74 1579—1590 Horiuti K, Somlyo AV, Goldman YE, Somlyo AP 1989 Kinetics of contraction initiated by flash photolysis of caged adenosine triphosphate in tonic and phasic smooth muscles. J Gen Physiol 94 769-781... 

Reversible electron transfer within Mg and Zn-substituted hemoglobin hybrids is initiated by flash photoproduction of the long-lived triplet state ( MP). According to Scheme I, the triplet return to the ground state involves two pathways, intrinsic triplet decay (with rate constant kp) and electron transfer quenching (with rate constant k,). 

Further information to help determine the CS2 oxidation mechanism comes from photochemical studies. Kondratiev and Yakovlevairradiated 16-55 torr CS2 in the presence of 40-100 torr O2 with light at 2000 A. The primary products were CS and S atoms. The major final products were SO2 and OCS, the latter undergoing further oxidation. Wright studied the isothermal, room temperature oxidation initiated by flash photolysis, as well as the flash photolysis of pure CS2. After flashing pure CS2, he observed the absorption spectra of CS and S2. The S2 disappeared rapidly, following second-order kinetics. CS was removed at the walls. In the presence of oxygen, the S2 was diminished, but its rate of disappearance was unaffected. SO2 and S2O absorption spectra were also... 

Some reactions of the OH radical, which can be initiated by flash photolysis, have been studied using resonance absorption to follow how the OH concentration varies with time. The reaction... 

Artificial photosynthesis was initiated by flash excitation of liposomes containing the triad and Qs, the quinone shuttle, using 5-ns, 430-nm flashes centered on the Soret band ofthe porphyrin. The sequence of events taking place upon photoexcitation is shown in Fig. 25 (B) right, where step involves photoexcitation of the artificial reaction center, P, the porphyrin, followed by charge separation and electron transfer, forming Q -P-C, which can be detected by the absorbance inaease due to the radical cation C. The yield ofQ -P-C was 0.1 and its lifetime was -110 in the absence ofQs and -60 ns in liposomes containing Qs. 

Electrochemical methods have also been adopted for application of high pressure [41-43] (see Chapter 5). Correlations emerging from these investigations have valuable application in the interpretation of partial molar volume changes associated with electron transfer reactions (see Sect. 1.3.4). A potential future interest is in reactions carried out at elevated pressures in a suprercritical fluid medium in view of this a special optical cell has been developed for studying organometallic reactions initiated by flash photolysis in supercritical fluids [20] (see Chapters 12 to 14). 

One of the most important teclmiques for the study of gas-phase reactions is flash photolysis [8, ]. A reaction is initiated by absorption of an intense light pulse, originally generated from flash lamps (duration a=lp.s). Nowadays these have frequently been replaced by pulsed laser sources, with the shortest pulses of the order of a few femtoseconds [22, 64]. 

The conmron flash-lamp photolysis and often also laser-flash photolysis are based on photochemical processes that are initiated by the absorption of a photon, hv. The intensity of laser pulses can reach GW cm or even TW cm, where multiphoton processes become important. Figure B2.5.13 simnnarizes the different mechanisms of multiphoton excitation [75, 76, 112], The direct multiphoton absorption of mechanism (i) requires an odd number of photons to reach an excited atomic or molecular level in the case of strict electric dipole and parity selection rules [117],... 

In this work the development of mathematical model is done assuming simplifications of physico-chemical model of peroxide oxidation of the model system with the chemiluminesce intensity as the analytical signal. The mathematical model allows to describe basic stages of chemiluminescence process in vitro, namely spontaneous luminescence, slow and fast flashes due to initiating by chemical substances e.g. Fe +ions, chemiluminescent reaction at different stages of chain reactions evolution. 

Assay of luminescence activity. Luciferin solution (1 ml) is mixed with 1.2 ml of 0.5 M Tris buffer (pH 8.2) and 0.3 ml of luciferase solution. The luminescence reaction is initiated by the injection of 0.5 ml of 0.176 mM H2O2 to the luciferin-luciferase mixture. The light emission is characterized by a flash of light, followed by a rapid decay to a much lower steady-state level (Fig. 10.4.1). The maximum light intensity of the flash is taken as the measure of the luminescence activity. 

Initiation by Light. Neither Deb (quoted in Ref 19, p 111) nor the writer (Ref 47) could produce detonation of PETN exposed to high-intensity light. The writer used PETN cores at 0.8 to 1.5g/cc, with and without small additions of graphite (in attempts to increase light absorbency), in 1 /4 inch ID plastic holders, and exposed them up to around 25microsec to the radiation of Argon flash bombs (T=29000°K). 

In the flash photolysis technique a large population of ground state molecules are raised to an excited singlet state by the initial photolysis flash. In a time r (singlet lifetime) after the photolysis flash a certain proportion of... 

Dry mixtures of barium phosphinate and potassium chlorate bum rapidly with a feeble report if unconfined, but even under the slight confinement of enclosing in paper, a sharp explosion occurs. The mixture is readily initiated by sparks, impact or friction. A mixture of calcium phosphinate, potassium chlorate and quartz exploded during mixing. Mixtures of various phosphinates and chlorates have been proposed as explosives, but they are very sensitive to initiation by sparks, friction or shock. Admixture of powdered magnesium causes a brilliant flash on initiating the mixture. 

The photochemical dissociation of Me2Ge from 7,7-dimethyl-l,4,5,6-tetraphenyl-2,3-benzo-7-germanorbomadiene (14) has been studied by flash photolysis, low-temperature matrix isolation and CIDNP 3H NMR techniques30. The results suggest that a biradical (15) is formed as an intermediate species in the photoreaction. The biradical is initially formed in the singlet state, which undergoes conversion to the triplet state before irreversible decomposition to form Me2Ge and tetraphenylnaphthalene (TPN) (reaction 19). 

Detonators are used to detonate high explosives. Stab detonators are initiated by sharp firing pins and are used in explosive trains of different types of fuses. Flash detonators are initiated by flames produced by safety fuses, primers, or delay elements. A special type of flash detonator ignited by the flame of a safety fuse is called a blasting cap. Detonators are primarily composed of three types of explosives including sinoxid mixtures, lead azide-based mixtures, and mercury fulminate-based mixtures. 

An explosive device is initiated or detonated by an explosive train — an arrangement of explosive components by which the initial force from the primary explosive is transmitted and intensified until it reaches and sets off the main explosive composition. Most explosive trains contain a primary explosive as the first component. The second component in the train will depend on the type of initiation process required for the main explosive composition. If the main explosive composition is to be detonated, the second component of the train will burn to detonation so that it imparts a shockwave to the main composition. This type of explosive train is known as a detonator. Detonators can be initiated by electrical means, friction, flash, or percussion. 

---