The fluorine atom, being the most electronegative, strongly seeks the more positive nitrogen atom during photolysis. The chlorine atom also apparently prefers the nitrogenbonded configuration, but not as much as fluorine. Bromine, which is less electronegative than oxygen or nitrogen, favors the more negative oxygen atom with photolysis.It is also interesting to note the very small amount of ONOBr formed in the initial matrix deposit. In an earlier account,9 the 1714-cm'1 absorption of ONOC1 was found to be approximately twice as intense as the 1675-cm"1 absorption of C1N02 under identical conditions as the present study, although no quantitative significance could be inferred at that time. Subsequently, Niki et al.,16 in an infrared study of the gas phase reaction of chlorine atoms and N02, estimated that ONOC1 was formed initially at more than four times the rate of C1N02. The agreement between these two reports appears to be excellent. Fluorine atoms have also been shown to react with the oxygen atom of N02 to form ONOF at low temperatures with no activation energy. The present results, however, show very little initial ONOBr formation during matrix condensation, and it is not clear why a barrier to the direct formation of ONOBr should exist.Recently, Molina and Molina17 and Spencer andRowland10 have discounted the role of ONOC1 and ONOBr, respectively, as stratospheric halogen atom sinks because of the measured high photodissociation cross section of ONOC1 in the near-UV17 and the belief10 that ONOBr is not expected to be significantly more stable than ONOC1. The present results clearly show that ONOBr is the most stable of the halogen nitrites with respect to the corresponding nitryl halides. However, it is not clear from our work that ONOBr is more stable than ONOC1 since the photolysis behavior could be easily attributed to the instability of BrN02 as compared to C1N02. On the other hand, the present results certainly do not rule out the possibility that the stability of ONOBr in the presence of near-UV irradiation is greater than the stability of ONOC1.
The ionization of phenothiazine incorporated in micelles of sodium laurylsulfate in water by 347.1 nm light (3.57 eV photon energy) may by explained by rapid tunneling of an electron from excited phenothiazine through the double layer into unoccupied electronic redox levels of the systems aq/eaq−. Photoionization is promoted by duroquinone (DQ) which is also solubilized in the micelles. In such a system semiquinone anion and phenothiazine cation radicals are formed via fast (< ns) intramicellar electron transfer from excited PTH and a relatively slow (μs) transfer from PTH triplets to DQ. The presence of duroquinone in a micelle prevents photoejection of electrons from phenothiazine into the water. Ionization was also achieved in cationic micelles of cetyl‐trimethyl‐ammonium‐bromide in the presence of naphthoquinone sulfonate at the periphery of the micelles. The phenothiazine/micelle/water system is an example for the heterogeneous catalysis of water decomposition by light, and the phenothiazine/micelle/quinone/water system may be regarded as a simple model for electron transfer in the photosynthetic system.
The rates of establishment of the acid-base equilibria for the radical anions of benzaldehyde, benzamide, benzonitrile, benzophenone, p-cyanoacetophenone and fluorenone have been studied by pulse radiolysis. In each case a first order rate of reaction was observed with kobs = k'+k"[H+], the constants having values of k' = (0.3-7.8) x lo4 s-' and k" = (0.7-2.5) x 1O'O dm3 mol-l s-'. These rate constants are associated with the reaction of the radical anion with water (k') and H+ (k"). The nature of the radical ions involved is discussed.' G . Beck, Dissertation (TU Berlin, 1968).
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