Photochemical reactions involving electronically excited oxygen

1 PHOTOCHEMICAL REACTIONS INVOLVING ELECTRONICALLY EXCITED OXYGEN 

Excellent reviews of the photochemistry of oxygen are already available [116,414,643]. 

Molecular oxygen 02 (3 g) absorbs UV radiation below 2000 A. Absorption in the Schumann—Runge band range (1759—1950 A) causes excitation to one of the vibrational levels of the 02(3 ,p state. Light absorbed within this range may produce the reactions 

The energy available at wavelengths below 1342 A is sufficient to produce the dissociation 

Absorption within the forbidden Herzberg band, originating near 2454 A, gives the forbidden transition 

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Figure 7-11 and its caption (Crutzen, 1983) depict the most important of the gas phase and photochemical reactions in the atmosphere. Perhaps the single most important interaction involves the hydroxyl free radical, OH-. This extremely reactive radical is produced principally from the reactions of electronically excited atomic oxygen, 0( D), with water vapor. Photo-... 

Acetazolamide and chlorthalidone have also been shown to photosensitize the reduction of nitro blue tetrazolium in phosphate-buffered saline solution. The reaction is more efficient under deoxygenated conditions and in the presence of superoxide dismutase. These results indicate that direct electron transfer occurs from either the excited state of 7 or 8 to the substrate, especially oxygen. No doubt, superoxide ion could be involved as an intermediate when oxygen is present. On the basis of these results, a photochemical reaction mechanism of acetazolamide and nitro blue tetrazolium is postulated as shown in Figure 63.9. 

Topics which have formed the subjects of reviews this year include excited state chemistry within zeolites, photoredox reactions in organic synthesis, selectivity control in one-electron reduction, the photochemistry of fullerenes, photochemical P-450 oxygenation of cyclohexene with water sensitized by dihydroxy-coordinated (tetraphenylporphyrinato)antimony(V) hexafluorophosphate, bio-mimetic radical polycyclisations of isoprenoid polyalkenes initiated by photo-induced electron transfer, photoinduced electron transfer involving C o/CjoJ comparisons between the photoinduced electron transfer reactions of 50 and aromatic carbonyl compounds, recent advances in the chemistry of pyrrolidino-fullerenes, ° photoinduced electron transfer in donor-linked fullerenes," supra-molecular model systems,and within dendrimer architecture,photoinduced electron transfer reactions of homoquinones, amines, and azo compounds, photoinduced reactions of five-membered monoheterocyclic compounds of the indigo group, photochemical and polymerisation reactions in solid Qo, photo- and redox-active [2]rotaxanes and [2]catenanes, ° reactions of sulfides and sulfenic acid derivatives with 02( Ag), photoprocesses of sulfoxides and related compounds, semiconductor photocatalysts,chemical fixation and photoreduction of carbon dioxide by metal phthalocyanines, and multiporphyrins as photosynthetic models. 

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