Photolysis, condensed phase

A variety of experimental methods has been used to study the thermal chemistry of the unsaturated iron fragments produced by photolysis. For example, regeneration of 1Fe(CO)s was observed upon heating low-temperature matrices in which Fe(CO)5 had been photolyzed (35). These condensed-phase reactions are rather complex, as in some cases, components of the inert matrix may form adducts Fe(C0)4L or Fe(CO)sL (L = N2, Xe, CH4), so that the reaction observed is not simply CO addition to an unsaturated iron tetracarbonyl fragment. The same reactions were studied in the gas phase, using flash... 

Excited states can be formed by a variety of processes, of which the important ones are photolysis (light absorption), impact of electrons or heavy particles (radiolysis), and, especially in the condensed phase, ion neutralization. To these may be added processes such as energy transfer, dissociation from super-excited and ionized states, thermal processes, and chemical reaction. Following Brocklehurst [14], it is instructive to consider some of the direct processes giving excited states and their respective inverses. Thus luminescence is the inverse of light absorption, super-elastic collision is the inverse of charged particle impact excitation, and collisional deactivation is the inverse of the thermal process, etc. 

Rates and Activation Parameters. The first condensed-phase absolute rate measurement for a carbene-alkene addition was reported by Closs and Rabinow in 1976 flash lamp photolysis of diphenyldiazomethane generated (triplet) diphenylcarbene, which added to butadiene (in benzene) with k =... 

In 1-octene solution, the following products are observed (21) a mixture of cis and trans 2-octene, a hydrocarbon of the formula C16H34, 2-octyl cyclohexanone, a compound of the formula C22H42O believed to be formed by the addition of 2 molecules of 1-octene to 1 molecule of the ketone, and a compound of formula C3oH6S0 believed to be formed by the addition of 3 molecules of 1-octene to 1 molecule of cyclohexanone. In addition, a considerable amount of a polymer is also formed. The complex mixture of products clearly indicates the difficulties in the study of photolysis in the condensed phase, particularly if it is necessary to determine the mechanism of the formation of the various products. 

Diffuse-Reflectance Laser-Hash Photolysis, in Photochemistry in Condensed Phases Kelly, G.P., Wilkinson, F. Scaiano, J.C. Ed. CRC Press, (1989). 

Depending on the pH of the ambient cloudwater, the Fe(III) hexaquo species of reaction 95 will hydrolyze to produce Fe(H20)50H2+ which is also photo-chemically active. In this regard Faust and co-workers [ 154,155] have investigated the photolysis of Fe(H20)50H2+as another potential source of hydroxyl radical in the condensed phases in the atmosphere. 

Among xenon oxides only XeOs and Xe04 have been definitively isolated and characterized. XeO is known, as a gas-phase species, to be bound with respect to a D(0) atom but not with respect to ground-state P(0). There is no evidence for a condensed phase XeO species. Recently, however, the unique radical, HXeO, has been isolated by UV photolysis of either H20/Xe or N20/HBr/Xe solid mixtures as 7K. The compound was characterized by IR and its intrinsic stability supported by ab initio calculations. ... 

As long as all of the reactions occur in the gas phase, we need not consider medium effects. For thermolysis or photolysis reactions that occur in condensed phases the medium may substantially alter the reactivity and must be considered in discussion of analogies. We will discuss each of the perturbations above in the following paragraphs. 

Products. Photolysis of 1,3-cyclohexadiene gives rise to 1,3,5-hexatriene of unknown stereochemistry. During irradiation in the condensed phase initial product is the m-triene which subsequently isomerizes photochemically. The other primary processes which seem to originate directly in 1,3-cydohexadiene are dehydrogenation ... 

Since, in a fluid medium, a molecule undergoes collisions with surrounding molecules at time intervals of sec. or less, photolysis of a compound in the condensed phase should produce the same results as photolysis at very high pressures in the gas phase. In line with this reasoning, photolysis of 1,3-cyclohexadiene in solution leads to very little benzene or C2 hydrocarbons. 1,3,5-Hexatriene is reported as the major product. The reverse reaction, viz. the cyclization of 1,3,5-hexatriene, is not observed in the condensed phase.In the gas phase, the net reaction... 

The condensed phase photolyses of COS have also been studied. Liquid solutions of COS in ethylene, propylene, isobutane, etc., at room temperature, upon photolysis afford characteristic singlet state products, although in somewhat diminished relative yields as compared to gas phase photolyses (vide infra). Solutions of COS in propylene irradiated in the solid phase at liquid nitrogen temperature also yield charac-... 

We have mentioned in the preceding section that the condensed phase photolysis of COS also affords S( D) atoms. This is evidenced by the... 

The condensed phase photolysis can be utilized advantageously for synthetic-preparative purposes. 

The condensed phase photolysis was studied with ethylene and propylene. A liquid solution of COS in ethylene (1 2.8 mole ratio), irradiated with an Hg-arc at room temperature, gave vinyl mercaptan and ethylene episulfide in a mole ratio of 0.43 1.00. In the gas phase reaction the corresponding value was 0.90 1.00. 

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