UV photodecomposition

The development of phase masks using the refractive index variation due to the UV-photodecomposition of the polysilane was examined.134 The refractive index due to UV-photodecomposition of PMPS changes from 1.70 to 1.56. The refractive index variation in PMPS films by UV-light irradiation is shown in Figure 31. 

Poon C. and Vittimberga B. M., UV photodecomposition of color in dyeing wastewater . Industrial waste, Processing of 13 th Mid-Atlantic Conference. 427-433. (1981)... 

Photochemical decomposition of riboflavin in neutral or acid solution gives lumichrome (3), 7,8-dimethyl all oxazine, which was synthesized and characterized by Karrer and his co-workers in 1934 (11). In alkaline solution, the irradiation product is lumiflavin (4), 7,8,10-trimethyhsoalloxazine its uv—vis absorption spectmm resembles that of riboflavin. It was prepared and characterized in 1933 (5). Another photodecomposition product of riboflavin is 7,8-dimethy1-10-foTmylmethy1isoa11oxazine (12). 

Diacyl peroxides have continuous weak absorptions in the UV to ca 280 nm (e ca 50 M cm 1 at 234 nm),147 Although the overall chemistry in thermolysis and photolysis may appear similar, substantially higher yields of phenyl radical products are obtained when BPO is decomposed photochemically. It has been suggested that, during the photodecomposition of BPO, (3-scission may occur in... 

Trichlorodibenzo-p-dioxin was sensitive to photodecomposition. When this compound was irradiated in TFMS acid by UV light, the upper spectrum in Figure 9 was obtained. However a new spectrum appeared after standing for a day, identical to the spectrum of the 1-chloro derivative. Further photochemical studies with this compound are being made. 

Fujishima and Honda [16, 158] reported the photodecomposition of water using semiconductor photoelectrolysis cells (Figure 4.10). When the surface of the Ti02 electrode was irradiated with UV light, oxygen evolution was observed at the Ti02 electrode surface and hydrogen at the Pt black electrode. The overall water photodecomposition reaction ... 

A UV analysis of the products formed upon photolysis of 2a at 280 nm in ethyl propionate, PMMA, and PPMA further illustrates the effect of the matrix stiffness on the photodecomposition process (Table III). The ratio 0C to b +, j [ c/( b+ d)) is determined by the ratio of absorbance of product 2c to the absorbances of products 2b and 2d [A2c/(A2b+A2d)1 n this case, since the results were tabulated from the actual absorption spectra (difference spectra), the ratio of the products formed in the solvent ethyl propionate can be directly compared to the ratios in PPMA and PMMA. From Table III, it is readily seen that the ratio increases on going from the ethyl propionate solution,... 

The irradiation of a polymer surface with the high intensity, pulsed, fer-UV radiation of the excimer laser causes spontaneous vaporization of the excited volume. This phenomenon was first described by Srinivasan (1) and called ablative photodecomposition. The attention of many researchers was drawn to the exceptional capabilities of photoablation (2). Etching is confined to the irradiated volume, which can be microscopic or even of submicron dimensions, on heat-sensitive substrates like polymers. In most experimental conditions, there is no macroscopic evidence of thermal damage, even when small volumes are excited with pulses of... 

When an aqueous solution containing 1,2-dichlorobenzene (190 pM) and a nonionic surfactant micelle (Brij 58, a polyoxyethylene cetyl ether) was illuminated by a photoreactor equipped with 253.7-nm monochromatic UV lamps, photoisomerization took place yielding 1,3- and 1,4-dichlorobenzene as the principal products. The half-life for this reaction, based on the first-order photodecomposition rate of 1.35 x lO Vsec, is 8.6 min (Chu and Jafvert, 1994). 

Photolytlc. The dye-sensitized photodecomposition of ametryn was studied in aqueous, aerated solutions (Rejto et al, 1983). When an aqueous ametryn solution was irradiated in sunlight for several hours, 2-(methylthio)-4-(isopropylamino)-6-amino-5-triazine and 2-(methylthio)-4-(iso-propylamino)-6-acetamido-5-triazine formed in yields of 55 and 2.6%, respectively. Continued irradiation of the solution led to the formation of 2-(methylthio)-4,6-diamino-5-triazine which eventually decomposed to unidentified products (Rejto et al., 1983). The UV (7, = 253.7 nm) photolysis of ametryn in water, methanol, ethanol, n-butanol, and benzene yielded the 2-//analog 4-(ethylamino)-6-isopropylamino-5-triazine. Photodegradation was not observed at wavelengths >300 nm (Pape and Zabik, 1970). 

An aqueous solution of amitrole can decompose in the following free radical systems Fenton s reagent, UV irradiation, and riboflavin-sensitized photodecomposition (Plimmer et al, 1967). Amitrole-5- C reacted with Fenton s reagent to give radiolabeled carbon dioxide, unlabeled urea, and unlabeled cyanamide. Significant degradation of amitrole was observed when an aqueous solution was irradiated by a sunlamp (L = 280-310 nm). In addition to ring compounds, it was postulated that other products may have formed from the polymerization of amitrole free radicals (Plimmer et al., 1967). 

Photodecomposition products included acidic compounds and five methylated derivatives (Plimmer, 1970). When picloram in an aqueous solution (25 °C) was exposed by a high intensity monochromatic UV lamp, dechlorination occurred yielding 4-amino-3,5-dichloro-6-hydroxy-picolinic acid which underwent decarboxylation to give 4-amino-3,5-dichloropyridin-2-ol. In addition, decarboxylation of picloram yielded 2,3,5-trichloro-4-pyridylamine which may undergo dechlorination yielding 4-amino-3,5-dichloro-6-hydroxypicolinic acid (Burkhard and Guth, 1979). 

When prometryn in aqueous solution was exposed to UV light for 3 h, the herbicide was completely converted to hydroxypropazine. Irradiation of soil suspensions containing prometryn was found to be more resistant to photodecomposition. About 75% of the applied amount was converted to hydroxypropazine after 72 h of exposure (Khan, 1982). The UV (A = 253.7 nm) photolysis of prometryn in water, methanol, ethanol, /i-butanol, and benzene yielded 2-methylthio-4,6-bis(isopropylamino)-s-triazine. At wavelengths >300 nm, photodegradation was not observed (Pape and Zabik, 1970). Khan and Gamble (1983) also studied the UV irradiation (A = 253.7 nm) of prometryn in distilled water and dissolved humic substances. In distilled water, 2-hydroxy-4,6-bis(isopropylamino)-5-triazine and 4,6-bis(isopropylamino)-5-triazine formed as major products. 

When propoxur in ethanol was irradiated by UV light, only one unidentified cholinesterase inhibitor formed. Exposure to sunlight for 3 h yielded no photodecomposition products (Crosby et ah, 1965). 

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