Water vapor, photolysis, decomposition

There would appear to be no difference in the reactions expected photo-chemically as the primary products are H atoms and OH radicals in both the electric discharge and on irradiation. Chen and Taylor (22) state that there is no evidence for oxygen atoms either in the photolysis or in the decomposition of water vapor in an electric discharge. However, the secondary formation of O atoms (2) and the formation of ozone (31, 50) in an electric discharge through water vapor have been demonstrated. It might be expected that under the proper experimental conditions similar results could be obtained photochemically. 

Apart from photosynthesis, photolysis can be a source of oxygen in the atmosphere (i.e., the decomposition of water vapor under the influence of UV radiation in the upper layers of the atmosphere). However, the intensity of this source under present conditions is negligible. Nevertheless, let us denote this flux by // = aH WA, where WA is water vapor content in the atmosphere and aH is an empirical coefficient. If we assume that in the upper layers of the atmosphere a constant share of WA can reside, then at H° = 0.0039102 km-2 yr and WA= 0.025m, we have aH = 1.56 10 7 per year. 

Laboratory experience had convinced chemists earlier that the Chapman mechanism needed a supplement of additional reactions. In 1960, McGrath and Norrish discovered the formation of OH radicals in the reaction of water vapor with 0( D) atoms generated by the photolysis of ozone, and they proposed a chain decomposition of ozone by water radicals. Meinel (1950) had previously demonstrated the existence of OH in the upper... 

No information was found on the transformation of diisopropyl methylphosphonate in the atmosphere. Based on the results of environmental fate studies of diisopropyl methylphosphonate in distilled water and natural water, photolysis (either direct or indirect) is not important in the transformation of diisopropyl methylphosphonate in aquatic systems (Spanggord et al. 1979). The ultraviolet and infrared laser-induced photodegradation of diisopropyl methylphosphonate in both the vapor or liquid phase has been demonstrated (Radziemski 1981). Light hydrocarbon gases were the principal decomposition products. Hydrogen, carbon monoxide (CO), carbon dioxide (C02), and water were also detected. 

Decomposition of l-methyl-2-pyrrolidinone (67) was studied by vapor-phase photolysis (72JA8281). Irradiation (Hg sensitized) led, in addition to extensive polymer formation, to the following products carbon monoxide (31%), ethene (24%), water (24%), l,3,5-trimethyl-hexahydro-l,3,5-triazine (8%), 1-methylazetidine (6%), 1-methylpyrrole, and methane (<1%). The mechanism of formation of most of these products involves... 

In the ambient atmosphere, NDMA should be rapidly degraded upon exposure to sunlight. The half-life for direct photolysis of NDMA vapor is on the order of 5 to 30 minutes. In surface water exposed to sunlight, NDMA would also be subject to photolysis. On soil surfaces, NDMA would be subject to removal by photolysis and volatilization. The volatilization half-life of NDMA from soil surfaces under field conditions has been found hours. In subsurface soil and in water beyond the penetration NDMA would be susceptible to slow microbial decomposition under both aerobic and anaerobic conditions. In aerobic subsurface soil, the half-life of NDMA has been found to be about 50 to 55 days. Degradation has been found to proceed slightly faster under aerobic conditions than under anaerobic conditions. 

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