Photolysis kinetics

Fig. 21. Photolysis kinetics of nitroxalkylcobalamin. A 10-4 M solution was photo-lyzed aerobically in the spectrometer cavity. The increase in maximum intensity of the high field line is shown as a function of time...

The reaction volume (AF°) for Fe +aq FeOH "aq + H" "aq is +4.8cm mol (extrapolated to zero ionic strength A V° decreases significantly with increasing ionic strength, to reach a value of +1.6cm mol at 7=2.0moldm . Laser flash photolysis kinetics indicate the formation of hydroxyl radicals in the primary photoprocess of FeOH " "aq photolysis. ... 

The photolysis kinetics has been determined according to the following equation which conforms to the pseudofirst order kinetic law with v being the photolysis velocity (Yeremin 1979) ... 

Fracton dimension was used to fit a photolysis kinetic of denatured HbNO shown below ... 

When referring to Ti02-based photocatalytic systems it is important to note that, in most cases, the semiconducting oxide is associated there with a noble metal or/and a noble metal oxide catalyst. While the role played by these catalysts in (partial) cathodic reactions seems relatively well understood it remains less clear with regard to the photoanodic reactions. In particular, the exact function of the extensively used ruthenium dioxide catalyst has been questioned The role of Ru02 as a hole-transfer catalyst has, for example, been established through laser-photolysis kinetic studies in the case of photo-oxidation of halide (Br and CP) ions in colloidal titanium dioxide dispersions. In fact, the yields of Brf and ClJ radical anions, photogenerated in the course of these reactions. 

It has been shown [14,15] that AIBN may be successfully used in experiments when in ruby laser s second harmonics (1=347nm) is being applied. It must be noticed that nanosecond laser impuls emission allows to obtain high concentrations of free radicals in solutions. But in cited and in [16-18] investigations the photolysis kinetics as well the specificities of laser absorption by matter are not studied. 

However, the similarity in bond strengths of the peroxide linkage to molecular 02, the ease with which the known -peroxo Cobalt complexes liberate 02 (in contrast to /x-oxo bipyridyl Mn dimers) on photolysis, kinetic barriers on ju-oxo to peroxo dimer conversions led Sawyer et al.47 -49) to suggest peroxo binuclear complexes as the most probable intermediates. More studies with model compounds are needed to elucidate this point. Various mechanisms proposed for water oxidations are variations of these two principal types. 

Another aspect and possibly another solution to the issue comes from work by Friedman using flash photolysis kinetics (of CO rebinding after photodissociation from ferrous P450 3A4). The kinetics were multiphasic and were selectively altered by the presence of different substrates. Heterotropic effects were observed with benzo[a]-pyrene and aNF. The interpretation of the results is that different substrates differentially modulate these kinetics by (a) changing the P450... 

Belous et al. [238] investigated the role of impurities as they affect luminescence and photolysis of silver azide. Subsequent to X-ray irradiation, luminescence appeared on UV excitation and was associated with the same interstitial Ag ions which influence the photolysis kinetics. By studying the growth of luminescence, it was concluded that the migration of energy to centers where decomposition occurs is via excitons, presumably excited anion states. 

The abbreviations used for techniques are DF-RF discharge flow-resonance fluorescence DF-RA discharge flow-resonance absorption DF-ESR discharge flow-esr detection DF-LMR discharge flow with laser magnetic resonance detection of OH DF-MS discharge flow-mass spectrometry FP-KS flash photolysis-kinetic spectroscopy FP-RA flash photolysis-resonance absorption FP-RF flash photolysis-resonance fluorescence MPS modulation-phase shift ... 

Several investigators at this laboratory over the last few years have studied the photodecomposition of picloram in aqueous solutions exposed to sunlight. Picloram concentrations were reduced to approach the maximum expected in the environment, yet kept high enough to measure accurately. Our analysis of the photolysis kinetics for these experiments and the resulting pseudo first-order rates found are presented below. 

The purpose of this study is to explore the fate of OH radicals and the identity and chemistry of their progeny in seawater. This paper presents some of the experimental evidence concerning radical formation and behavior in seawater and artificial seawater obtained by the fast-reaction kinetics technique of flash photolysis-kinetic spectrophotometry (4) supplemented by pulse radiolysis ( ). The companion paper which follows presents results on related reactions and rates observed in media simpler than seawater and applies them to partially explain the data reported here using a simple reaction-mechanistic model. 

Zafiriou, 0. C. True. M. B. Flash photolysis - kinetic spectrophotometry of seawater and related solutions Data acquisition, processing, and validation," UHOI Tech. Memo. 1-77, Woods Hole Oceanographic Institution, 1977. 

Flash photolysis kinetic study of the equilibrium CH3O2 + NO2 = CH3O2NO2 Chem. Phys. Lett. 191 (1992) 259. 

Another aspect and possibly another solution to the issue comes from work by Friedman using flash photolysis kinetics (of CO rebinding after... 

The reaction of sulfate and phosphate radicals with a, a, a-trifluorotoluene has been studied by flash photolysis. Kinetic measurements and the nature of the possible intermediate organic radicals were discussed. ... 

Acid aquation of [Rh(tren)Cl2] gives a-[Rh(tren)(OH2)Cl] " base hydrolysis gives 8-[Rh(tren)(OH)Cl] (as indeed does photolysis). Kinetics of base hydrolysis of these three complexes are detailed. " Acid aquation of [Rh(NH3)5(N02)] results in ammonia loss (see above), but base hydrolysis results in loss of nitrite. " ... 

Trentham, D. R., Corrie, J. E. T. Reid, G. P. (1992). A new caged ATP with rapid photolysis kinetics. Biophysical Journal, 61, A295. 

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