Photolysis photodegradation quantum yield

During photolysis, the double bond content of the polysilane(P-l)(15mol% in this experiment) decreased to 10mol%, as measured by 1H-NMR spectroscopy. However, the ratio, quantum yield of scission(Q(S))/quantum yield of crosslinking(Q(X)), was not affected by the reaction of the double bond. West and his coworkers have reported that poly((2-(3-cyclohexenyl)-ethyl)methylsilane-co-methylphenylsilane) crosslinked upon irradiation(55). The difference between our results and West s may lie in the amount of the double bond and inhibitation of the radical closslinking by the phenol moiety. Polysilane with a halogen moiety, P-8, photodecomposed rapidly, compared with P-1 or P-3. The introduction of a chloride moiety was effective for the sensitization of the photodegradation. Similar results has already been reported(55). 

Photolytic. Dalapon (free acid) is subject to photodegradation. When an aqueous solution (0.25 M) was irradiated with UV light at 253.7 nm at 49 °C, 70% degraded in 7 h. Pyruvic acid is formed which is subsequently decarboxylated to acetaldehyde, carbon dioxide, and small quantities of 1,1-dichloroethane (2-4%) and a water-insoluble polymer (Kenaga, 1974). The photolysis of an aqueous solution of dalapon (free acid) by UV light (X = 2537 A) yielded chloride ions, carbon dioxide, carbon monoxide, and methyl chloride at quantum yields of 0.29, 0.10, 0.02, and 0.02, respectively (Baxter and Johnston, 1968). 

Bopp L, Boucher O, Aumont O, Belviso S, Dufresne JL, Pham M, Monfray P (2004) Will marine dimethylsulfide emissions amplify or alleviate global warming A model study. Can J Fish Aquat Sci 61 826-835 Bouillon RC, Miller WL (2004) Determination of apparent quantum yield spectra of DMS photo-degradation in an in situ iron-induced Northeast Pacific Ocean bloom. Geophys. Res. Lett. 31 Article no. L06310 Bouillon RC, Miller WL (2005) Photodegradation of dimethyl sulfide (DMS) in natural waters Laboratory assessment of the nitrate-photolysis-induced DMS oxidation. Environ Sci Technol 39 9471-9477... 

UV-Vis absorption spectroscopy is the most widely used technique in the study of drug photochemistry. The instrument is inexpensive and easy to use. Concentrations of the drug and its product can be easily monitored by this method because they normally have distinct spectra. Not only the rate of photodegradation but also the quantum yield for the process is determined in some cases. Moreover, the excited state responsible for the reaction can be ascertained by carrying out photolysis in... 

Photolysis of polyphenylvinylketone at 365 nm in benzene solution or in the solid state results in a decrease in the molecular weight of the polymer [6], The quantum yield of this process (irradiation at 313 nm) has been estimated to be 0.25 [Ref. 60] or 0.22 [Ref. 61] in solution. Since no carbon monoxide resulting from the Norrish type I split could be detected, the Norrish type II scission is considered to be responsible for the photodegradation of polyphenylvinylketone [6] namely,... 

The effect of concentration, temperature, and solvent on the photodegradation of benzothiazolinospiropyrans using flash photolysis has been presented. trans-Cyclo-octene is shown to be the major product in the photolysis of m-cyclo-octene with a quantum yield of 0.34. Hamanoue and co-workers " report on intersystem crossing and lowest triplet states of 4-chromanone, chromone, and flavone and of some nitroanthracene derivatives." For the latter long build-up times for triplet-triplet absorption were observed (72—86 psec) and represent the effect of the rates of internal conversion T aa/ T,). Indirect intersystem crossing to higher levels of the triplet manifold is most important in these systems. 

More recently, Gupta and coworkers (4,5), using the same PnBA samples as were used in the present study. Investigated photodegradation at 293°K and 77°K with radiation of 253.7 nm and 310 nm. They Identified certain principal photoproducts and measured their quantum yields of formation. The data obtained from a number of different experimental methods were used to formulate a mechanism of photolysis of PnBA which has a close relationship to the results of this present study. 

Subst- rate No. Initial concentration of the starting dioxin, P o (10" M) Maximum irradiation time, max (h) Average percentage disappearance of the starting dioxin after max (%) Photolysis first-order rate constant k P (10 sec Absolute half-life , % (h) Quantum yield for the photodegradation. 

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