Hydrocarbons excited, decomposition

On the other hand, the formation of ethylene was ascribed mainly to the unimolecular decomposition of a neutral excited propane molecule. These interpretations were later confirmed (4) by examining the effect of an applied electrical field on the neutral products in the radiolysis of propane. The yields of those products which were originally ascribed to ion-molecule reactions remained unchanged when the field strength was increased in the saturation current region while the yields of hydrocarbon products, which were ascribed to the decomposition of neutral excited propane molecules, increased several fold because of increased excitation by electron impact. In various recent radiolysis 14,17,18,34) and photoionization studies 26) of hydrocarbons, the origins of products from ion-molecule reactions or neutral excited molecule decompositions have been determined using the applied field technique. However, because of recent advances in vacuum ultraviolet photolysis and ion-molecule reaction kinetics, the technique used in the above studies has become somewhat superfluous. 

The rate of the chain reaction of hydrocarbon decomposition is proportional to the product of concentrations of chain carriers and excited molecules responsible for chain propagation (Zaikin 2008 Zaikin and Zaikina 2008) ... 

The resulting products, such as sulfenic acid or sulfur dioxide, are reactive and induce an acid-catalyzed breakdown of hydroperoxides. The important role of intermediate molecular sulfur has been reported [68-72]. Zinc (or other metal) forms a precipitate composed of ZnO and ZnS04. The decomposition of ROOH by dialkyl thiophosphates is an autocata-lytic process. The interaction of ROOH with zinc dialkyl thiophosphate gives rise to free radicals, due to which this reaction accelerates oxidation of hydrocarbons, excites CL during oxidation of ethylbenzene, and intensifies the consumption of acceptors, e.g., stable nitroxyl radicals [68], The induction period is often absent because of the rapid formation of intermediates, and the kinetics of decomposition is described by a simple bimolecular kinetic equation... 

No photolyses of hexahydro-1,2,4,5-tetrazines have been published. The kinetics of the photodecomposition of 1,3,5-triphenylverdazyl (61) was studied by Soviet authors in various hydrocarbons. The rate depends on the solvent. The excited radical is consumed by H extraction from the solvent and by dissociation at the N—N bond, forming the product 1,3-diphenyl-l,2,4-triazole (138), which catalyzes the decomposition of the verdazyl radical (74IZV2204). The dipole moment of (61) in the excited state is 9 1 D in the ground state it is 2.94 D. 

By exciting the red-orange cyclooctatetraene dianion 1 in the presence of cyclooctatetraene in our photoelectrochemical cell (n-TiC>2/NH3/Pt), we were able to observe photocurrents without detectable decomposition of the anionic absorber (2). Presumably, a rapid dismutation of the photooxidized product inhibited electron recombination, producing a stable hydrocarbon whose cathodic reduction at the counter electrode regenerates the original mixture essentially quantitatively (eqn 3). 

The complexes [Cu(S2CNEt2]2] and [Cu S2P(OPr )2 2] have been shown to be extremely effective scavengers for peroxy radicals and can be used to inhibit the autoxidation of hydrocarbons.99 Poly(2,6-dimethyl-1,4-phenylene oxide) can be effectively stabilized against thermal degradation by the bistriazene complex (41).100 The stabilizing action is thought to involve quenching of thermally excited states and the decomposition of hydroperoxides by the complex. 

Studies on a range of saturated hydrocarbons indicate that the main decomposition reactions of electronically excited alkane molecules formed by electron impact are118,122-124... 

Let us briefly overview the results of relevant studies. The mechanism of the photolysis of hydrocarbon peroxide radicals of different types was studied [119], and the decomposition of the electron-excited peroxide fragment with an 0-0 bond cleavage was found to be the primary act of the process. When the reaction is not complicated by the adsorption of molecules on the solid surface, its kinetic parameters can be determined. The rate constants of the reactions of radicals =Si, =Si-0-0, =Si-CH, =Si-0-CH, =Si-CH2-CH, and =Si-0- C = O with H2(D2), CH4, C2H6, and C3H8 were measured in Ref. [16]. 

The study of the production of excited states by the thermolysis of 1,2-dioxetanes is quite extensive (e.g. Nakamura and Goto, 1979a,b). It has been found that the addition of electron donors, e.g. amines and aromatic hydrocarbons (in the ground state), accelerate the decomposition. The process has... 

The photolysis of n-butane follows a pattern similar to that of propane, with many corresponding reactions. As found for previous hydrocarbons the photolysis includes both molecular and free-radical processes. The molecular elimination of Hj and Dj from C4H10-C4D10 mixtures was first shown by Sauer and Dorfman, who concluded that at 1470 A more than 90 % of the hydrogen came from molecular processes. On the basis of a study of the decomposition of excited -butane molecules generated by electron impact , they attributed hydrogen, methane, ethylene, and other hydrocarbon products to molecular processes, and concluded that free-radical reactions were minimal. 

The main conclusion to be drawn from the application of the benzene photosensitization method to the decomposition of cyclobutanone is that the Cj-hydrocarbons originate from the low-lying triplet state of the ketone. However, use of this method in the investigation of cyclopentanone decomposition indicated that reactions I, II and III (if it is a separate primary process) occur from the first excited state of the ketone. This conclusion was based on the quantitative agreement found between the pressure dependence of the decarbonylation-product formation and the fluorescence quenching by cyclopentanone. 

In a later paper, Lewis and Saunders observed that triplet quenchers (cis-piperylene, oxygen) failed to affect the course of the direct photolysis of alkyl azides, from which it was concluded that the photolysis proceeded via a singlet azide and singlet nitrene. This was further supported by the observation that hexyl azide acted as an efficient quencher of aromatic hydrocarbon fluorescence, and that this singlet sensitization of hexyl azide led to the decomposition of the azide with an efficiency similar to that of direct photolysis Thus, although triplet sensitization leads to decomposition of alkyl azides, it appears that direct photolysis proceeds by way of an excited singlet azide without intersystem crossing to the triplet. 

In aromatic azides ° the mechanism of the primary step is slighdy different from that of the isolated azido group. Here the upper excited states are those of the parent hydrocarbon and, on irradiation, energy is absorbed in the aromatic system as a whole. Decomposition is therefore preceded by a transfer of excitation from the hydrocarbon to the azido group. How this comes about will be described on the example of 1-azidonaphthalene (see Figure 3 where the potential energy curves of the RN—N2 bond are shown for the singlet states of this molecule). 

The efficient light-initiated decomposition of azides has been the basis for commercially important photoresist formulations for the semiconductor industry. A common approach is to mix a diazide, such as diazadibenzylidenecyclohexanone (I), with an unsaturated hydrocarbon polymer. Excitation of the difunction-al sensitizer produces highly reactive nitrenes which crosslink the polymer by a variety of paths including insertion into both carbon-carbon double bonds and carbon-hydrogen bonds, and by generation of radicals. The polymer component in the most widely used resists is polyisoprene which has been partially eye Iized by reaction with p-toluenesulfonic acid G). Other polymers used include polycyclopentadiene and the copolymer of cyclopentadiene and a-methyI styrene ( ). 

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