Pulse photolysis

The growth of long chains ( > 10 ) in the perfectly mixed 1 1 crystals of ethylene with chlorine and bromine at 20-70 K was studied in detail by Wight et al. [1993]. Active radicals were generated by pulse photolysis of CI2 or Br2. The rate constant was found to be /Cc = 8-12s below Tc = 45 K. The chain grows according to the well known radical mechanism including the reactions... 

In this article we have summarized the use of both photochemical and more classical thermal kinetics techniques to deduce the nature of intermediates in the ambient temperature, fluid solution chemistry of several triruthenium clusters. In some cases the photochemically generated intermediates appear to be the same as those proposed to be formed along thermal reaction coordinates, while in other cases unique pathways are the results of electronic excitation. The use of pulse photolysis methodology allows direct observation, and the measurement of the reaction dynamics of such transients and provides quantitative evaluation of the absolute reactivities of these species. In some cases, detailed complementary information regarding... 

The reaction of the peroxyl radical with the sulfonyl radical was studied by pulse photolysis technique [38]. Both radicals were generated photochemically by a light pulse (A = 270 -380 nm) in the system DBP-cyc/o-CgHnSCkCI ryc/o-CgH lRH) air (T 293 K). The reactions of free radical formation were the following ... 

Walker JW, Somlyo AV, Goldman YE, Somlyo AP, Trentham DR 1987 Kinetics of smooth and skeletal muscle activation by laser pulse photolysis of caged inositol 1,4,5-trisphosphate. Nature 327 249-251... 

Niu L, Abood LG, Hess GP (1995) Cocaine mechanism of inhibition of a muscle acetylcholine receptor studied by a laser-pulse photolysis technique. Proc Natl Acad Sci USA 92 12008-12012... 

The experiments of Kistiakowsky and Kydd [1] were done by single-pulse photolysis with a 500-J flashlamp, the reaction vessel contents being sampled via a pinhole leak into the electron ionization source of a Bendix time-of-flight (TOF) mass spectrometer. Mass spectra were obtained by pulsed extraction of ions from the ion source at 50-fis intervals after the flash. The signal from the electron multiplier detector was displayed on a cathode ray tube, which was photographed with a rotating drum camera. 

Highly exothermic chemical reactions can give ions as products. Such reactions are called chemi-ionization reactions. When one or more of the reactants are formed by pulsed photolysis, and the ion product(s) are time-resolved with a mass spectrometer, this comprises a FPTRMS experiment. The ions can be extracted by a biased pair of electrodes, one of which has an aperture through which ions pass to enter a quadrupole mass spectrometer. The time resolution of this experiment is superior to FPTRMS experiments between neutrals, since the ion velocities are set by the electrode bias voltage, and the thermal molecular velocity distribution limitation is no longer a factor. With modest electrode bias voltages, the detection time can be as short as 2 /is. 

Figure 3. Quantum yield for the laser pulse photolysis of iodine in ethane at gaseous, supercritical fluid, and liquid densities.

Quantitative investigations of the photoinduced electron transfer from excited Ru(II) (bpy)3 to MV2 + were made in Ref. [54], in which the effect of temperature has been studied by steady state and pulse photolysis techniques. The parameters ve and ae were found in Ref. [54] by fitting the experimental data on kinetics of the excited Ru(II) (bpy)3 decay with the kinetic equation of the Eq. (8) type. It was found that ae did not depend on temperature and was equal to 4.2 + 0.2 A. The frequency factor vc decreased about four orders of magnitude with decreasing the temperature down to 77 K, but the Arrhenius plot for W was not linear, as is shown in Fig. 9. 

A detailed discussion on the pyrolysis and photolysis of SCBs and pyrolysis of germacyclobutanes can be found in the CHEC-II(1996) <1996CHEC-II(1B)867>. Pyrolysis of SCBs at 500-700 °C yields silenes en route to 1,3-disilacyclo-butanes, ethylene being the predominant component of the gaseous reaction products (Scheme 1). Gas-phase and laser-pulsed photolysis proceed in the same way. 

The question of the multiplicity of the reactive state in the photolysis of a-germyl ketones is rather controversial. An attempt to apply laser pulse photolysis techniques... 

From this perspective, the combination of spin chemistry techniques and laser pulse photolysis should allow one to obtain the most valuable information on the formation and decay reactions of such active short-lived derivatives as alkyl-substituted germylenes and digermenes, as well as on germanium-centered free radicals67,68. 

In this work the authors summarize their own studies of photoprocesses on CdS colloids with particles of various size. In these studies, attention was given precisely to photocatalytic reactions on CdS, the photocatalytic reactions on TiC>2 were considered concurrently with the reported ones. In most cases photocatalytic reactions on semiconductors are the redox reactions. So of special interest was to study the regularities of reactions of interfacial transfer of photoexcited electron by the pulse photolysis and luminescence quenching methods. Many interesting phenomena were found while studying the model photocatalytic reactions by the method of stationary photolysis, i.e., under the conditions of real photocatalysis. 

The in-situ growth of Pt clusters during photodeposition leaves little doubt that the electronic interaction between Pt and TiC>2 in photodeposited Pt-islands is stronger than in physically mixed ones. Thus, the former is expected to exhibit a stronger promotion effect than the latter under the same specific conditions. This has been verified by the CW photolysis in the presence of O2 and repetitive laser-pulse photolysis in the absence of O2 [82]. 

Cornu et al. investigated the quantum yield, 4>f, of photocatalytic formate oxidation in oxygenated acidic Ti02 suspension under continuous and periodic pulse illumination [91]. For very short illumination times in periodic pulse photolysis, Cornu et al. demonstrated that 4>f was identical to the value obtained under continuous illumination at the same time-averaged photon absorption rate. This is in sharp contrast to the results of Wang et al. for photocatalytic methanol oxidation [82],... 

Photochromism of 4-nitro-, 6-nitro-, and 4,6-dinitro-5-methylbenzimidazole bases and their quaternary salts has been examined by pulse photolysis [1404], Generated neutral medium anions of aci-nitroacids have, in case of compounds with 4-nitro groups, the lifetimes 3 orders more than those of 6-nitroisomers [1404],... 

Li, G., Pei, W., and Niu, L. (2003). Ghannel opening kinetics of GluR2Qflip AMPA receptor A laser-pulse photolysis study. Biochem. 42, 12358-12366. 

While it is difficult to ensure the rehable observation of the radical processes during the mixing of reagents, these are easily detected in the photoinduced reactions of aryl-substituted compounds of Ge and Sn. Laser pulse photolysis experiments show that direct photoionization of Ph3Ge(Sn) anion results in the neutral radical . The apphcation of the Chemically Induced Dynamic Electron Polarization (CIDEP) method has allowed the detection of polarized emission signal of the radicals, thus leading to a conclusion that direct photoionization of Ph3Ge(Sn) anion occurs from the triplet state (equation 7). ... 

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