Photolysis steady-state

Product analysis has been useful in deciding the preferred path. Quantum yields for Co(II) production (number of molecules produced/number of quanta absorbed) measured by steady-state photolysis of CofNHj) " and Cofen) " are 0.45 and 0.11 respectively. These show that exclusive electron transfer (when the quantum yield would be 1.0) does not occur. ... 

The photocatalytic system is shown in Scheme 5, where BNAH is oxidized by the ZnP + moiety in the radical ion pair ZaP -Ceo (ki) produced upon photoirradiation of ZnP-Ceo, whereas HV " is reduced to HV by the Ceo" moiety of ZnP +-C6o ki). These individual electron-transfer processes compete, however, with the BET in the radical ion pair (/cbet)- This pathway was experimentally confirmed by photolysis of the ZnP-Ceo/BNAH/HV and ZnP-H2P-C6o/BNAH/HV + systems with visible light (433 nm) in deoxyge-nated PhCN [70], For instance. Fig. 4 depicts the steady-state photolysis in deoxy-genated PhCN, in which the HV absorption band (X ax = 402 and 615 nm) increases progressively with irradiation time. By contrast, no reaction occurs in the dark or in the absence of the photocatalyst (i.e., ZnP-Ceo or ZnP-H2P-C6o) under photoirradiation [70]. Once HV+ is generated in the photochemical reaction, it was found to be stable in deoxygenated PhCN. The stoichiometry of the reaction is established as given by Eq. (3), where BNAH acts as a two-electron donor to reduce two equivalents of HV [70] ... 

Usually, experiments are performed with steady-state photolysis or radiolysis of the solution and the yield of scavenger products determined optically or by ESR methods. There is no direct interest in the actual time evolution of the density or recombination (survival) probability. Consequently, the creation of ion-pairs may be pictured as occurring at a constant rate, say 1 s 1, from time t0 = 0 to infinity. The steady-state ion-pair density distribution, which arises when dp/dt = 0, is the balance between continuous creation of ion pairs at a rate Is-1, recombination and scavenging. Removing the instantaneous creation of an ion-pair at time t = t0 (i.e. removing the 6(f — f0) in the source term), means that ion-pairs were continuously formed from time t = — 00 to t. At long times, f > — oo the density distribution is independent of t and, of course, t0. Let pss(r cs r0) = /i p(r, t cs t0, 0)d 0 be the steady-state ion-pair density distribution for ion pairs continuously formed at r0, and note d/dt J" f pd 0 = 0. The diffusion equation (169) becomes... 

The direct detection of O( >) by the emission at 63(X) A in the steady state photolysis of C02 near 1470 A has failed [Young and Ung (1067), Clark and Noxon (216)], although O( >) atoms from 02 photolysis near 1470 A have been detected. The failure to detect the emission must be due to the weak absorption of C02, rapid quenching of O( D) by C02, and the long radiative life of O( D) atoms. However, the production of O( D) in the C02 photolysis is strongly indicated by the following observations ... 

Mortensen A, Skibsted LH (1998) Reactivity of p-carotene towards peroxyl radicals studied by laser flash and steady-state photolysis. FEBS Lett 426 392-396 Munoz F, von Sonntag C (2000) The reactions of ozone with tertiary amines including thecomplex-ing agents nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA) in aqueous solution. J Chem Soc Perkin Trans 2 2029-2033... 

Intense labor is usually required in the search for experimental conditions leading to the stoichiometric relationship illustrated in Equation 6.42. This search for the optimum conditions can be greatly ameliorated when the steady-state photolysis is used in conjunction with flash photochemical techniques. 

However, agreement between studies is poor and the overall mechanism of oxidation is unclear, although SO2, methane sulfonic add (MSA), and dimethyl sulfone (DMSO2) have been identified as stable end products in steady state photolysis experiments (19-22). 

Steady-state photolysis (Ray-o-Net) of 7-methoxy-l, 1,3,3,7-pentamethyl-8-oxa-2-thia-5,6-diazaspiro[3,4]oct-5-ene 9 in cyclohexane at 300 nm followed by GC-MS analysis of the resulting mixture showed the formation of 3-isopropy-lidene-2,2-dimethylthiirane 20 as a product of the rearrangement of 2,2,4,4-tetramethyl-3-thietan-l-ylidene 6 (Scheme 4). The second product observed from the photolysis of 9 had strong peaks in the mass spectrum at m/z... 

For steady-state photolysis and flash photolysis at comparatively low flash intensity one can easily obtain the conditions, under which no more than one pair of Ru(bpy) + and C16V+ particles is generated at a time at the inner surface of the vesicle membrane, and all the processes with the participation of these particles are completed long before the next light quantum reaches the vesicle. In this case one may describe the recombination kinetics by the first order kinetic law [111] with the rate constant ... 

Bavykin, Dmitry V. is a Ph.D. researcher in the Laboratory of photocatalysis on semiconductors at the Boreskov Institute of Catalysis, Novosibirsk, Russia. The title of his PhD thesis (1998) Luminescent and photocatalytic properties of CdS nanocolloids . Area of his interests is the photophysical-photochemical properties of nanosized sulfide semiconductors, including synthesis of particles with definite size and surface properties, their characterisation the study of the photoexcited states dynamics, relaxation in quantum dots by the luminescence and flash photolysis measurements studies of the interfacial charge transfer from colloidal semiconductor particles by the steady state photolysis, luminescence quenching method. 

Figure 8A Diffuse reflectance spectra recorded following the steady-state photolysis (visible light) of Acid Orange 7 adsorbed on Ti02 nanoparticles (0.02 mmol A07/g of Ti02). The ordinate scale is expressed in Kubelka-Munk units, where R is the reflectivity measured at the corresponding wavelength. (From Ref. 258.)...

Figure 9 In situ diffuse reflectance FTIR spectra of A07 on Ti02 surface (0.10 mmoles of A07/g of Ti02) during steady-state photolysis. The spectra were recorded at time intervals of (a) 0, (b) 60 min, and (c) 24 h of irradiation with visible light. (From Ref. 258.)...

In the early 1970s, van Tamelen and co-workers reported on the steady state photolysis of several stabilized carbocations [69-72], The reactions were often complex, and very dependent on the solvent conditions. Although no electron donors were deliberately added, the nature of the products occasionally suggested an electron transfer process had taken place. For instance, when triphenylcyclopro-... 

Cyclic trisilane 323 upon steady-state photolysis (245 nm) was used for preparation of diphenylsilylene 324, the silicon analogue of singlet diphenylcarbene <2006JA14442>. Diphenylsilylene 324 was trapped by MeOH or triethylsilane to give diphenylmethoxysilane 325 and l,l,l-triethyl-2,2-diphenyldisilane 326 in 72 and 69% yield, respectively. 

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