Vacuum Ultraviolet Photolysis of Trimethylethylene (original) (raw)
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Gas phase photolysis of 1-butene at 147 nm (8.4 eV)
Journal of Photochemistry, 1978
The photolysis of 1-butene was carried out in a static system using the xenon resonance line at 147 nm (8.4 eV) at pressures in the range 15-500 Tort (2-66.5 kPa). The major products observed were acetylene, ethane, ethylene, allene, propyne, 1,3-butadiene and isopentane. The radical species were identified by using scavengers such as oxygen and H2S. Evidence is presented for the occurrence of ten primary processes to which quantum yields have been ascribed. The main process is a 13 cleavage of the CC bond which occurs with a yield of ~ = 0.51. A hydrogen atom mechanism involving the occurrence of hot hydrogen atoms (about 30% of them have an excess energy of about 0.26 eV) was proposed to account for the pressure dependence of propylene. Dissociation of excited radicals contributes to the formation of allene and propyne.
Canadian Journal of Chemistry, 1978
A systematic study of the pressure effects on the quantum yields of some products between 0.1 and 600 Torr (13 and 80 000 N m−2) was carried out in the 7.6 and 8.4 eV photolysis of normal, iso- and cis-2-butenes. The propylene quantum yield (s-C4H9* → C3H6 + CH3) decreased with the increase in the n-butene pressure and a good linearity of S/D (stabilization/decomposition) vs. pressure plot, over a broad pressure region, was observed. It is concluded that hydrogen atoms involved in the s-C4H9* radical formation are produced with a relatively narrow energy distribution. The slope of S/D vs. pressure lines decreased with the increase in photon energy, indicating the trend in the kinetic energy of the H-atoms.In the case of isobutene and cis-2-butene photolysis, the Stern–Volmer plots for allene formation were nonlinear. It is concluded that the formation of two different allene precursors is needed to account for this result. By the use of a simple RRK-type formalism we also conclude t...
Vacuum UV photolysis of n-1-hexene and 4-methyl-1-pentene
Journal of Photochemistry, 1980
We studied the vacuum UV photolysis of n-l-hexene and 4-methyll-pentene at 147,163 and 174 nm. In both systems the use of NO or 06 and DI indicates that the main fragmentation process (a = 0.8) of the 147 nm photoexcited molecule is the breaking of the C-C bond located at the p position. This process leads to the formation of ally1 and propyl radicals. The propyl radicals decompose further at low pressure, giving rise to the formation of ethylene or propylene. By following the pressure effect on the ethylene or propylene quantum yields, and using RRKM results, it is shown that the n-propyl radicals formed in the n-1-hexene photolysis carry less energy than would be expected from a statistical distribution of the excess energy. The situation seems to be more complex for 4-methyl-l-pentene, and the isopropyl radicals have an energy content not far from the statistical distribution.
The vacuum UV photolysis of 1-hexene and 1-hexyne
Journal of Photochemistry, 1983
A comparative study was made of the photolysis of l-hexene and l-hexyue at 184.9 and 147 run. Three primary processes were observed in each system. They are, in decreasing order of importance, the rupture of the p(C-C) bond, the rupture of the y(C-C) bond and the retro-ene process. Thus the behaviour of both photoexcited molecules is similar to a first approximation. However, there are meaningful differences. In particular, the rupture of the y(C-C) bond is relatively more important in the l-hexyne case and leads to the formation of vinylacetylene at 147 nm. This observation suggests that the r(C-C) rupture may be the result of isomerization of the photoexcited molecule (a l,3 hydrogen shift) which is followed by the rupture of the @(C-C) bond.
Gas phase photolysis of propylene at 8.4 and 10.0 eV
Journal of Photochemistry, 1982
The photolysis of gaseous propylene was carried out in a static system using the krypton (10 .O eV) and xenon (8.4 eV) resonance lines at pressures in the range 1-700 Torr. Only decomposition processes were studied and no attempt was made to establish the pattern of free-radical reactions. The primary decomposition channels were established. With increasing energy the contribution of the processes involving molecular elimination increases at the expense of simple scission of the C+Z and C-H bonds. A comparison of the present data with those obtained by CMin and coworkers at 7.6 eV reveals that in the range 7.6-10 .O eV the mechanism for dissociation changes completely. At 7.6 eV atomic hydrogen is formed, while at 10.0 eV this process is virtually absent being replaced by the formation of molecular hydrogen. Roth processes occur at an intermediate energy of 8.4 eV. The energy distribution among the products of the primary decomposition exhibits marked deviations from statistical randomization.
Photolysis of n-butene and isobutene at 174.3 – 174.5 nm (7.10 eV)
Journal of Photochemistry, 1978
The photolysis of n-butene and isobutene was carried out in a static system using nitrogen resonance lines at 174.3 -174.5 nm (7.11 -7.10 eV). The main fragmentation process of the photoexcited n-butene molecule is the C-C split in the fl position to the double bond. The primary quantum yield Cp is 0.66. The Q, value for the (x C-C split of isobutene is equal to 0.78.
The Journal of Chemical Physics, 2002
Photolysis of acetylene has been performed by vacuum-ultraviolet excitation with the synchrotron radiation via the Rydberg states converging to the first ionization potential ͑IP͒ at 11.4 eV. Only the visible fluorescence of the ethynyl radical was observed in the à 2 ⌸ -X 2 ⌺ ϩ system. Excitation of several Rydberg states of acetylene over a large energy range between 9 and 11.4 eV allowed us to observe for the first time the evolution of this continuum with increasing Rydberg excitation. Intensity calculations based on accurate ab initio potential energy surfaces of C 2 H were performed by using a one-dimensional model accounting for the large-amplitude motion of the H atom around the C-C bond and for the overall rotation of the radical. These calculations successfully reproduce the observed visible continuum ͑maximum at 500 nm and blue side cutoff at 400 nm͒ and bring new information on the distribution of the internal energy deposited in the fragment. For most excited Rydberg states, predissociation occurs in a rather low time scale, leaving the C 2 H fragment in the à state, vibrationally hot, mostly with significant excitation in the bending mode around the isomerization barrier.
Journal of the American Chemical Society, 2009
The reactions of the methylidyne radical (CH) with ethylene, acetylene, allene, and methylacetylene are studied at room temperature using tunable vacuum ultraviolet (VUV) photoionization and time-resolved mass spectrometry. The CH radicals are prepared by 248 nm multiphoton photolysis of CHBr3 at 298 K and react with the selected hydrocarbon in a helium gas flow. Analysis of photoionization efficiency versus VUV photon wavelength permits isomerspecific detection of the reaction products and allows estimation of the reaction product branching ratios. The reactions proceed by either CH insertion or addition followed by H atom elimination from the intermediate adduct. In the CH + C2H4 reaction the C3H5 intermediate decays by H atom loss to yield 70(+-8)percent allene, 30(+-8)percent methylacetylene and less than 10percent cyclopropene, in agreement with previous RRKM results. In the CH + acetylene reaction, detection of mainly the cyclic C3H2 isomer is contrary to a previous RRKM calculation that predicted linear triplet propargylene to be 90percent of the total H-atom co-products. High-level CBS-APNO quantum calculations and RRKM calculation for the CH + C2H2 reaction presented in this manuscript predict a higher contribution of the cyclic C3H2 (27.0percent) versus triplet propargylene (63.5percent) than these earlier predictions. Extensive calculations on the C3H3 and C3H2D system combined with experimental isotope ratios for the CD + C2H2 reaction indicate eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide.