Methane solid, photolysis

Quantum yields for photochemically induced low-temperature reactions are also sensitive to intermolecular effects (i.e., the structure of the solid). For example, the quantum yield for reaction (9.15) in glassy mixtures of methane and chlorine at 20 K varies from 0.1 to 0.001, depending on the method of sample preparation [Benderskii et al., 1983]. The lowest values are obtained for samples prepared by thermal or ultrasonic annealing prior to UV photolysis. 

The photolysis of pure methane in the solid phase and of methane in argon or krypton matrices has been examined by Ausloos et at 1236 A. The photolysis of solid methane is very similar to the gas-phase photolysis. Hydrogen and ethane are the major products, with CH4-CD4 mixtures showing an H2 and D2 richness over HD, and a predominance of d, d, d and rfg fractions in ethane. These features are indicative of molecular elimination of hydrogen followed by insertion of CH2 into methane. It was found that the smaller but significant contribution of ethane- s was greater than that of either ethane- i or d. This has been interpreted as evidence for the primary photolysis of methane into a hydrogen atom and a methyl radical. The fact that little ethane- i or is found excludes the formation of the methyl radicals by the dissociation of a hot ethane molecule after insertion by CH2. The minor products of photolysis are ethylene, propane, butanes, propene and pentanes. The presence of ethylene-[Pg.68]

Photolysis of phenyl and o-trifluoromethylphenyl azide in solid matrices led to the triplet nitrene as detected by e.s.r. The actual processes involved in aromatic azide photolyses have been the subject of much studyThe electronic spectra of the nitrenes were measured by photolysis of a number of aryl azides in organic matrices at 77°K . These species were stable indefinitely at this temperature, no change being observed in the spectra for hours. The photolysis of diazides at 77°K, whether conjugated (e.g. / -diazido-benzene) or not [e.g. bis (j6-azidophenyl) methane] proceeded in two distinct steps to the dinitrene. The second step was about two to three times as efficient as the first ( 2/ 1 2-3)... 

Scheffer and co-workers have carried out extensive research on the use of oiganic salts for, e.g asymmetric synthesis (Schemes 36-38), heavy atom effects (Scheme 39), and triplet sensitization (Scheme 40) [43a,64-73]. Chiral crystals of prochiral oiganic acids or bases were prepared by salt formation with optically active amines or acids, respectively, and the solid-state photochemistry of the resultant salts led to asymmetric induction in prochiral acids or bases. These are illustrated for the solid-state di-7C-methane photoreaction of 9,10-ethenoanthra-cene (dibenzobarrelene) derivatives (Schemes 36 and 37) [65-67] and for the Norrish type II photocylization of phenyl ketones (Scheme 38) [68-71]. Nonab-soibing, optically active amines or acids must be used as a chiral handle. Solution photolysis gave photoproducts with no optical activity. 

The photochemical decomposition of methanal in a solid Xe matrix has been studied. Work has also been reported dealing with the photodissociation dynamics of methanal, and ab initio calculations have been carried out on the photochemical decomposition of acetaldehyde into methane and CO. The photocatalytic decomposition of acetaldehyde to yield carbon dioxide has also been reported. The threshold for CC bond fission in propanal and the release of the CHO fragment has been shown to be at a wavelength of 326.26 nm. Chowdhury has reported the dissociation of propynal using multiphoton irradiation. Gas-phase photolysis of butyraldehyde in the 280-330 nm range has shown that the CHO radical is produced. ... 

In(CO)2, and In(CO)2-In (Scheme 21). Additionally, InMe and GaMe have been reported via the reaction of the respective group 13 atoms with methane in solid Ar matrix. The products are formed via UV photolysis (X = 200-400 nm) to give the alkylmetalhydride followed by photodissociation on broad-band irradiation (k = 200-800 nm) to yield MeM(I) derivative. 

Irradiation using 0.8 MeV proton irradiation or far-UV photolysis at 10—20K of polar and apolar ices rich in CO2, containing acetylene or methane with analysis by IR, gave evidence for ketene formation, which was proposed to occur by free radical processes. Reagents labeled with and were used in most of the experiments, since the normal ketene asymmetric stretch is nearly coincident with the solid CO fundamental vibration near 2136 cm . A major route for ketene formation from acetylene was assigned to reaction with oxygen atoms (Eqn (4.15)). Acetamide (CH3CONH2) has an abundance in space comparable to that... 

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