Acetone, photolysis

Fig. 3.20. Conductivity of ZnO film

The study [39] shows that similar equation is valid for adsorption of NH- and NH2-radicaIs, too. There are a lot of experimental data lending support to the validity of the proposed two-phase scheme of free radical chemisorbtion on semiconductor oxides. It is worth noting that the stationary concentration of free radicals during the experiments conducted was around 10 to 10 particles per 1 cm of gas volume, i.e. the number of particle incident on 1 cm of adsorbent surface was only 10 per second. Regarding the number of collisions of molecules of initial substance, it was around 10 for experiments with acetone photolysis or pyrolysis provided that acetone vapour pressure was 0,1 to 0,01 Torr. Thus, adsorbed radicals easily interact at moderate temperatures not only with each other but also with molecules which reduces the stationary concentration of adsorbed radicals to an even greater extent. As we know now [45] this concentration is established due to the competition between the adsorption of radicals and their interaction with each other as well as with molecules of initial substance in the adsorbed layer (ketones, hydrazines, etc.). 

Warneck, P. and Zerbach, T. Synthesis of peroxyacetyl niUate in air by acetone photolysis, Environ. Sci. Technol, 26(1) 74-79, 1992. 

FIGURE 6.36 (a) Measured OH concentrations as a function of altitude and model-predicted concentrations without acetone photolysis and with acetone photolysis, respectively, (b) Calculated rates of HOx production from O, and acetone photolysis, respectively, as a function of altitude. (Adapted from Wennberg et at., 1998.)... 

The past decade has been an extremely fruitful one in the field of quantitative free radical kinetics. Two papers can be identified as the starting point of much of this work. The first of these is the acetone photolysis study by Noyes and Dorfman1 which gave confidence to the use of acetone as a reproducible source of methyl free radicals in a fairly simple kinetic environment. The second is the study of Gomer and Kistiakow-sky2 of the absolute rate of recombination of CH3 radicals. The latter study made it possible to give absolute values for the Arrhenius parameters for the reactions of alkyl free radicals with stable molecules. It also opened the way for putting the reactions of methyl radicals with other alkyl radicals on an absolute basis. 

One of the very striking features of the acetone photolysis is the absence... 

Acetone photolysis at 253.7 and 313 nm studied to test 515 the validity of the stationary state approximation 193 and 248 nm photodissociation of acrylic acid and 516 methacrylic acid shown to result in decarboxylation and formation of carbenes. Energy disposal in the COj fragments probed using i.r. fluorescence... 

By analogy with acetone photolysis which produces mainly carbon monoxide and ethane, two types of primary process are likely for the photolysis of halogenated ketones... 

QUANTUM YIELDS OF ACETONE PHOTOLYSIS AT 3130 A BASED ON THE RESULTS OF Larson and O Neal as well as on those of Heicklen and Noyes ... 

Fig. 11. The pressure dependence of the quantum yields of ihemain products of acetone photolysis at 2800 A and at high intensities (/ 10 quanta.l". sec" ).------,P torr acetone ------,...

Fig. 14. The dependence of the quantum yields of acetone photolysis on the intensity at 3130 A and 50 torr . O, "AczHs > co =...

DEPENDENCE OF THE CjHe/CO RATIO FROM ACETONE PHOTOLYSIS ON THE INTENSITY OF RADIATION AT 2537 A, 25 C AND 50 TORR PRESSURE... 

Methyl ethyl ketone was detected in experiments above lOO C. Acetonyl acetone has not been identified in the products so far. Actually, not more than a small amount of this compound is expected to be formed, since (i) the acetyl radical is unstable at higher temperatures, and (ii) the rate of formation of acetonyl radical is slow at lower temperatures. The formation of biacetonyl was observed in the investigation of the reaction between CH3 and acetone . Brin-ton ° has succeeded in detecting biacetonyl also among the products of acetone photolysis in the temperature range 200-475°C. Most of the evidence on the formation of biacetonyl in the photolysis of acetone is, however, based on material bal-ance and hence is only of secondary importance. 

No gas products were reported to be formed in earlier investigations of liquid acetone photolysis -however, the formation of CO, CH4 and C2H6 was established later - . These gas products were also observed - with inert solvents such as fluorinated hydrocarbons and water. The quantum yields obtained in liquid acetone and in inert solvents are in reasonable agreement (Table 18), indicating similarities in the mechanisms. 

VALUES OF Ei2—iE26 and of ki2lk26 at 25 °C, obtained from acetone photolysis IN THE CONDENSED PHASE... 

This class of organic emissions is exemplified by acetone and its higher homologues. As for the aldehydes, photolysis and reaction with the OH radical are the major atmospheric loss processes (Atkinson, 1989). The limited experimental data available indicate that, with the exception of acetone, photolysis is probably of minor importance. Reaction with the OH radical is then the major tropospheric loss process. For example, for... 

The marked decrease in the formation of hydrogen and methane under oxygen implies the presence of hydrogen atoms and methyl radicals. Most of the products and their distribution are similar to those of acetone photolysis. The two exceptions are 2-methylpropylene glycol and 2-hydroxy-2-methylpropanal, both of which arise from the 2-hydroxy-... 

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