Photolysis acetylene

The ground state C1(Xl L ) is a primary product of acetylene photolysis. The r/ ll state is formed from the photolysis of bromoacetylene in the vacuum ultraviolet. It is also formed in flame and discharges through carbon containing compounds. The Swan system is a major feature of emission spectrum from the heads of comets. 

The ground stale ) is a primary product of acetylene photolysis. 

This slice in velocity space can also be resolved by core-extraction methods. Changing the polarization of the probe laser will core out a different part of the two-dimensional slice. These core-extraction experiments were recently done by Lai et al. [100] on acetylene photolysis at... 

The CH emission accounts for 1% of the total observed emission and requires 12.76 eV of energy which compares to the 12.84 eV provided by two ArF laser photons. It is interesting to note that Metzger and Cook observed visible emission in the 300-600 nm region as a function of acetylene photolysis wavelength between 103 and 58 nm. Between 103 and 92 nm there is a sudden onset of visible fluorescence. This region corresponds very closely to the thermodynamic threshold for... 

Irradiation of ethyleneimine (341,342) with light of short wavelength ia the gas phase has been carried out direcdy and with sensitization (343—349). Photolysis products found were hydrogen, nitrogen, ethylene, ammonium, saturated hydrocarbons (methane, ethane, propane, / -butane), and the dimer of the ethyleneimino radical. The nature and the amount of the reaction products is highly dependent on the conditions used. For example, the photoproducts identified ia a fast flow photoreactor iacluded hydrocyanic acid and acetonitrile (345), ia addition to those found ia a steady state system. The reaction of hydrogen radicals with ethyleneimine results ia the formation of hydrocyanic acid ia addition to methane (350). Important processes ia the photolysis of ethyleneimine are nitrene extmsion and homolysis of the N—H bond, as suggested and simulated by ab initio SCF calculations (351). The occurrence of ethyleneimine as an iatermediate ia the photolytic formation of hydrocyanic acid from acetylene and ammonia ia the atmosphere of the planet Jupiter has been postulated (352), but is disputed (353). 

Electronic excitation from atom-transfer reactions appears to be relatively uncommon, with most such reactions producing chemiluminescence from vibrationaHy excited ground states (188—191). Examples include reactions of oxygen atoms with carbon disulfide (190), acetylene (191), or methylene (190), all of which produce emission from vibrationaHy excited carbon monoxide. When such reactions are carried out at very low pressure (13 mPa (lO " torr)), energy transfer is diminished, as with molecular beam experiments, so that the distribution of vibrational and rotational energies in the products can be discerned (189). Laser emission at 5 p.m has been obtained from the reaction of methylene and oxygen initiated by flash photolysis of a mixture of SO2, 2 2 6 (1 )-... 

Photochemistry. Vinyl chloride is subject to photodissociation. Photexcitation at 193 nm results in the elimination of HCl molecules and Cl atoms in an approximately 1.1 1 ratio (69). Both vinyUdene ( B2) [2143-69-3] and acetylene have been observed as photolysis products (70), as have H2 molecules (71) and H atoms [12385-13-6] (72). HCl and vinyUdene appear to be formed via a concerted 1,1 elimination from excited vinyl chloride (70). An adiabatic recoil mechanism seems likely for Cl atom elimination (73). As expected from the relative stabiUties of the 1- and 2-chlorovinyl radicals [50663-45-1 and 57095-76-8], H atoms are preferentially produced by detachment from the P carbon (72). Finally, a migration mechanism appears to play a significant role in H2 elimination (71). 

The photolysis of chlorodiazirine was investigated in several cases. From chloromethyl-diazirine (232) vinyl chloride was formed as the stable primary product of stabilization of chloromethylcarbene, with acetylene and hydrogen chloride as secondary products. Some 1,1-dichloroethane was assumed to have been formed through a linear diazo compound by reaction with HCl. Added HBr yielded 1-bromo-l-chloroethane (76MI5Q800). 

Similarly, low-temperature photolysis of 4,5,6-fluorosubstituted 1,2,3-tna zines results in the elimination of nitrogen, but the product composition depends on the substituents When the substituents are fluonne atoms, the intermediate product IS a four-membered, mtrogen-contaming ring that quickly dimenzes When all the substituents are perfluoroalkyl groups, the pyrolysis results in a mixture perfluoroalkyl acetylenes and perfluoroalkyl cyanides [79] (equations 48 and 49). 

Tile following photochemical conversions also involve 1,2-dithietes as intermediates whose chemical trapping was reported in most cases. Tlie formation of the dithiin 249 from 250 may best be explained by the formation of the dithiete dimer 251 and the loss of S2 (73ZC424).Tlie formation of 252 and 253 from 254 (78NJC331) should be compared with the sulfuration of the acetylene 182 with elemental sulfur (93BCJ623).Tlie photolysis of 255 provides a rare example when the ejection of a nitrile was employed for the generation of a 1,2-dithiete (73ZC431). 

In the analogous studies of the photolysis of sulfolane (31), the work of Honda and coworkers66 was carried out in the gas phase at 70-130 °C and established the formation of S02, ethylene, cyclobutane and acetylene as the major products, on mercury-sensitized photolysis. In considerable contrast, photolysis of sulfolane at 185 nm in the liquid phase67 produced ethylene( = 0.22), the sultine (32) (parallel experiments on aqueous solutions of sulfolane, a sulfinic acid is also believed to be formed. The authors believe that both four-membered (33) and six-membered (32) sultines may be formed during these photolyses. Further work in this area would appear to be necessary to unravel the full mechanistic details. 

The discovery that photolysis of hypochlorite (14) gave chloroketone (11) directly provided a short cut in this synthesis. The ketone in (11) will need to be protected during reaction with acetylene. 

A number of hydrocarbon radicals having multiple bonds at the radical centre have also been trapped in inert matrices and studied by IR spectroscopy. Thus, ethynyl radical was obtained by vacuum UV photolysis (9) of matrix-isolated acetylene (Shepherd and Graham, 1987) as well as when acetylene and argon atoms excited in a microwave discharge were codeposited at 12 K (Jacox and Olson, 1987). An appearance of diacetylene bands was observed when the matrices were warmed up, while the absorptions of the radical C2H disappeared. Detailed isotopic studies of D-and C-labelled ethynyl radicals showed a surprisingly low frequency of the C=C bond stretching vibration at 1846 cm instead of c.2100cm for a true C=C triple bond (the band at 2104 cm was attributed to the... 

The main difficulty in obtaining the vinyl radical is that the species easily loses the hydrogen atom and is converted into acetylene. Nevertheless, a very low concentration of the radical H2C=CH has been achieved (Shepherd et al., 1988) by vacuum UV photolysis of ethylene frozen in an argon matrix, and a Fourier transform IR study of this intermediate has been carried out. A variety of and deuterium-substituted ethylene parent molecules were used to form various isotopomers of vinyl radical. On the basis of its isotopic behaviour and by comparison with ab initio... 

As an example of application of semiconductor sensors for this purpose, we consider photolysis of simplest olefines (ethylene, propylene, acetylene, etc.) occurring in the range of vacuum ultraviolet. It is well-known (e.g., see [11]) that photolysis of ethylene may result in detachment of either hydrogen molecules (detached in one act) or hydrogen atoms. Hydrogen atoms subsequently associate into molecules or interact with ethylene molecules. In what follows, we consider how this problem can be solved with the help of sensors. 

To monitor a possible influence of molecular products of photolysis of ethylene (acetylene, ethane, and butane) on the sensor, a second sensor was positioned at a distance of 50 cm from the photolysis zone. The second sensor was designed to introduce corrections into the readings of the movable sensor. The specified distance was chosen so that atoms and radicals produced in the lower part of the vessel could not reach the... 

Gas-phase photolysis of diazoethane results in mixtures of ethylene, acetylene, and cis- and frans-2-butene. A mechanism involving the initial formation of ethylidene followed by formation of activated ethylene [which is collisionally deactivated or decomposes to produce acetylene and hydrogen— Eqs. (11.26(b,c,d)] or alternate attack on diazoethane to produce 2-butene [Eq. 11.26(e)] is proposed ... 

Methylene cyclopropene (5), the simplest triafulvene, is predicted to be of very low stability. From different MO calculations5 it has been estimated to possess only minor resonance stabilization ranging to 1 j3. Its high index of free valency4 at the exocyclic carbon atom causes an extreme tendency to polymerize, a process favored additionally by release of strain. Thus it is not surprising that only one attempt to prepare this elusive C4H4-hydrocarbon can be found in the literature. Photolysis and flash vacuum pyrolysis of cis-l-methylene-cyclopropene-2,3-dicarboxylic anhydride (58), however, did not yield methylene cyclopropene, but only vinyl acetylene as its (formal) product of isomerization in addition to small amounts of acetylene and methyl acetylene65 ... 

The compound 251 decarbonylates on photolysis to bis(4-hydroxyaryl) acetylene 253, which is easily oxidized to the quinonoid cumulene 254. This is also obtained by thermal decarbonylation of the product of oxidation of cyclopropenone 251, the diquinocyclopropanone 252. Likewise, the blue derivative of 3-radialene 256 (a phenylogue of triketo cyclopropane) is formed from tris-(4-hydroxyaryl) cyclopropenium cation 255 by oxidation34. ... 

Our next experience with a carbene was associated with the attempt to get 1,2-diphenylcyclobutadiene by photolysis of diphenylcyclopropenyldiazo-methane17. It was found that the (diphenylcyclopropenyl)carbene splits mainly into diphenylacetylene and acetylene and rearranges only to a very small extent to the wanted cyclobutadiene. 

In another study the kinetics and mechanism of an unprecedented T/2-vinyl isomerization of a highly fluorinated tungsten(II) metalla-cyclopropene complex was studied (92). Photolysis of a tungsten(II) tetrafluoroaryl metallacycle 1 and perfluoro-2-butyne results in the formation of the kinetic rf -vinyl complex 2 in which the fluoride is trans to the inserted acetylene and cis to both carbonyl ligands. Upon heating 2 is converted to the thermodynamic rf -vinyl complex 3 in which the fluoride ligand is now cis to the inserted alkyne and trans to one CO and cis to the second CO ligand as shown in Scheme 1. 

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