Photosensitization by Cd(3P1) Atoms. II. Gas Phase Decomposition of Cyclohexane

1972 ◽  
Vol 50 (13) ◽  
pp. 2010-2016 ◽  
Author(s):  
B. L. Kalra ◽  
A. R. Knight
Keyword(s):  
Quantum Yield ◽  
Gas Phase ◽  
Vapor Phase ◽  
Exposure Time ◽  
Molecular Hydrogen ◽  
Primary Decomposition ◽  
Phase Decomposition ◽  
Hydrogen Atoms ◽  
Hydrogen Formation ◽  
Volatile Products

The photodecomposition of cyclohexane sensitized by Cd(3P1) atoms has been studied in the vapor phase at 355 °C. The primary decomposition gives hydrogen atoms and cyclohexyl radicals. The volatile products of the decomposition are H2, cyclohexene, propylene, ethane, ethylene, methane, propane, butadiene, and methylcyclopentane. Products other than H2 and cyclo-C6H10 arise from unimolecular reactions of cyclohexyl radicals, the most important such process being the production of propylene and allyl radicals. Hydrogen yields decrease rapidly with time because of H-atom scavenging reactions involving olefinic products. The quantum yield of molecular hydrogen formation at the shortest exposure time examined is 0.53.

Photosensitization by Cd(3P0,1) atoms. III. Gas phase decomposition of cyclopentane

1976 ◽  
Vol 54 (1) ◽  
pp. 77-84 ◽  
Author(s):  
Bansi L. Kalra ◽  
Arthur R. Knight
Keyword(s):  
Gas Phase ◽  
Vapor Phase ◽  
Product Formation ◽  
Time Dependent ◽  
Primary Process ◽  
Phase Decomposition ◽  
Unimolecular Decomposition ◽  
Hydrogen Atoms ◽  
Volatile Products ◽  
Radical Decomposition

The triplet cadmium photosensitized decomposition of cyclopentane in the vapor phase has been studied at 355 °C and has been shown to give rise to cyclopentyl radicals and hydrogen atoms with close to unit efficiency in the primary process. Subsequent reactions of these species, including an important contribution from unimolecular decomposition of cyclopentyl radicals, yield the observed volatile products, hydrogen, methane, ethylene, ethane, propylene, and cyclopentene. As a result of significant olefin scavenging of H-atoms product yields are strongly time dependent. The system has been shown to be unaffected by addends. The temperature dependence of the rate of product formation is consistent with the known energetics of cyclopentyl radical decomposition.

The photolysis of 2,3- and 3,3-dimethyl-1-butene at 147.0 and 184.9 nm

1985 ◽  
Vol 63 (1) ◽  
pp. 62-67 ◽  
Author(s):  
Hélène Deslauriers ◽  
Guy J. Collin
Keyword(s):  
Quantum Yield ◽  
Gas Phase ◽  
Electronic State ◽  
Photon Energy ◽  
Low Pressure ◽  
Decomposition Process ◽  
Primary Decomposition ◽  
Primary Process ◽  
The One

The photofragmentation of 2,3-dimethylbutene and 3,3-dimethylbutene has been studied at 147 and 184.9 nm in the gas phase. The main primary decomposition process at both wavelengths involves the rupture of a β(C—C) bond. The quantum yield for this process is higher than 0.7 at 147 nm and is probably even higher at 184.9 nm. All dimethallyl radicals formed at 147 nm in this process decompose at low pressure, but some of them isomerize from the α,β- to the α,α- structure (and vice versa) — via a 1,4-H transfer — before decomposition. At 184.9 nm, the same primary process is used to get a rough value for the lifetime of the photoexcited molecule, compared with the one made with RRKM calculations by assuming that all the photon energy resides in the vibrational framework of the fundamental electronic state. These lifetimes are about one nanosecond or less.

Direct Photolysis of 2-Propanol Vapor

1972 ◽  
Vol 50 (14) ◽  
pp. 2217-2223 ◽  
Author(s):  
O. S. Herasymowych ◽  
A. R. Knight
Keyword(s):  
Quantum Yield ◽  
Wavelength Range ◽  
Exposure Time ◽  
Yield Enhancement ◽  
Quantum Yields ◽  
Unimolecular Decomposition ◽  
Direct Photolysis ◽  
Volatile Products ◽  
Temperature And Pressure

The photolysis of 2-propanol vapor in the 1800–2000 Å wavelength range has been investigated. The volatile products of the reaction and their quantum yields at 80 °C and 200 Torr substrate pressure are H2 (0.64), CH3COCH3 (0.34), CH4 (0.39), CH3CHO (0.29), CO (0.15), and C2H6 (0.08). A mechanism is proposed that accounts for the observed rate variations with substrate pressure, exposure time, temperature, and pressure of inert addend. Acetone and acetaldehyde undergo significant secondary decomposition and this is the source of CO, CH4, and C2H6. Acetaldehyde is formed in the unimolecular decomposition of C3H7O radicals produced in the primary process.The effects of CO2 and CF4 as inert addends have been examined and it has been established that the quantum yield enhancement through collision induced predissociation that has been reported to occur in methanol is not a characteristic of the 2-propanol photolysis.

scholarly journals Photoinduced polycyclic aromatic hydrocarbon dehydrogenation

2018 ◽  
Vol 616 ◽  
pp. A167 ◽  
Author(s):  
P. Castellanos ◽  
A. Candian ◽  
H. Andrews ◽  
A. G. G. M. Tielens
Keyword(s):  
Molecular Hydrogen ◽  
Dust Grains ◽  
Hydrogen Atoms ◽  
Hydrogen Formation ◽  
Polycyclic Aromatic ◽  
Low Efficiency ◽  
H2 Formation ◽  
Chemical Conditions ◽  
Far Ultraviolet ◽  
High Level

The physical and chemical conditions in photodissociation regions (PDRs) are largely determined by the influence of far ultraviolet radiation. Far-UV photons can efficiently dissociate molecular hydrogen, a process that must be balanced at the HI/H2 interface of the PDR. Given that reactions involving hydrogen atoms in the gas phase are highly inefficient under interstellar conditions, H2 formation models mostly rely on catalytic reactions on the surface of dust grains. Additionally, molecular hydrogen formation in polycyclic aromatic hydrocarbons (PAHs) through the Eley–Rideal mechanism has been considered as well, although it has been found to have low efficiency in PDR fronts. In a previous work, we have described the possibility of efficient H2 release from medium to large sized PAHs upon photodissociation, with the exact branching between H-/H2-loss reactions being molecule dependent. Here, we investigate the astrophysical relevance of this process, by using a model for the photofragmentation of PAHs under interstellar conditions. We focus on three PAHs cations (coronene, ovalene, and circumcoronene), which represent three possibilities in the branching of atomic and molecular hydrogen losses. We find that, for ovalene (H2-loss dominated) the rate coefficient for H2 formation reaches values of the same order as H2 formation in dust grains. This result suggests that this hitherto disregarded mechanism can account, at least partly, for the high level of molecular hydrogen formation in dense PDRs.

Primary process(es) in the mercury-photosensitized decomposition of dimethyl ether at 2537 Å

1968 ◽  
Vol 46 (16) ◽  
pp. 2693-2697 ◽  
Author(s):  
R. Payette ◽  
M. Bertrand ◽  
Y. Rousseau
Keyword(s):  
Carbon Monoxide ◽  
Quantum Yield ◽  
Light Intensity ◽  
Dimethyl Ether ◽  
Molecular Hydrogen ◽  
Room Temperature ◽  
Primary Process ◽  
Methyl Radicals ◽  
Hydrogen Atoms ◽  
Radical Recombination

The mercury-photosensitized decomposition of dimethyl ether has been studied at room temperature and at pressures ranging from 10 to 200 Torr.The formation of an excited dimethyl ether (DME) molecule has been verified by following the rates of formation of methane, ethane, and carbon monoxide with various ether pressures.The study of the variation of the quantum yield of molecular hydrogen formation with absorbed light intensity at high ether pressures has shown that the primary process involves the dissociation of ether molecules into hydrogen atoms and methoxy methyl radicals:[Formula: see text]The results presented in this paper indicate that the excited DME molecule can originate in a radical recombination between hydrogen atoms and methoxy methyl radicals.

Radiolysis of methylcyclohexane. III. Pure vapor phase and effects of additives

1967 ◽  
Vol 45 (14) ◽  
pp. 1649-1659 ◽  
Author(s):  
W. J. Holtslander ◽  
G. R. Freeman
Keyword(s):  
Vapor Phase ◽  
Secondary Reaction ◽  
Hydrogen Yield ◽  
Methyl Radicals ◽  
Hydrogen Atoms ◽  
Hydrogen Formation ◽  
Positive Ions ◽  
Total Ionization ◽  
Different Types ◽  
Increasing Temperature

The radiolysis of methylcyclohexene (MCH) vapor was carried out under a variety of conditions. The G-values of the main products at 110°, extrapolated to zero dose, are hydrogen (5.2), methylcyclohexene isomers (2.0), ethylene (1.5), methane (1.3), propylene (0.8), and total dimer (0.3). Other products were also measured.The hydrogen yield was reduced to G = 3.1 by each of the additives, N2O, SF6, and CCL4, and to G = 1.6 by C2H4. Both DI and ND3 increased the total hydrogen yield above the value in pure MCH. In pure MCH approximately 50% of the ions (G(total ionization) = 4.4) resulted in hydrogen formation, whereas in the presence of DI or ND3, 75% of the ions are hydrogen precursors. Thus three different types of positive ions are distinguished in the system: G(M1+) = 2.1, G(M2+) = 1.3, and G(N+) = 1.0.The average ion lifetime with respect to neutralization was 10−3 s. The ion DI−was therefore stable with respect to decomposition to D + I− for a period greater than 10–3 s under the conditions of the experiments (~380 Torr MCH, 110°).The yield of methylcyclohexene isomers increased with increasing temperature and increased upon addition of ND3 or C2H4 to the radiolysis system. The dimer yield was also enhanced by the addition of ND3. This effect was explained by the occurrence of an ionic secondary reaction that destroys methylcyclohexene and (or) methylcyclohexyl radicals in pure MCH.Approximately 85% of the methane is produced by methyl radicals abstracting hydrogen atoms from MCH.

The Role of Gas Phase Decomposition in the ALE Growth of III–V Compounds

1991 ◽  
Vol 222 ◽  
Author(s):  
K. G. Reid ◽  
H. M. Urdianyk ◽  
N. A. El-Masry ◽  
S. M. Bedair
Keyword(s):  
Boundary Layer ◽  
High Temperature ◽  
Gas Phase ◽  
Exposure Time ◽  
Growth Temperature ◽  
Phase Decomposition ◽  
Temperature Growth ◽  
Mocvd Reactor ◽  
Maximum Exposure

ABSTRACTThe effects of the growth temperature and exposure time to TMGa for ALE of gallium arsenide was studied using TMGa and AsH3 in a modified, vertical, atmospheric, MOCVD reactor with a rotating susceptor. It was found that the temperature range for ALE growth could -be extended from 450°C to 700°C by adjustment of the exposure time to TMGa. The maximum exposure time to TMGa was found to decrease as growth temperature increased with high temperature growth limited to exposures of only fractions of a second. Beyond a critical exposure time to TMGa, gallium droplets form on the surface. It is known that premature decomposition of TMGa in the heated gaseous boundary layer causes the formation of the gallium droplets and the consequent loss of ALE growth.

Excited radicals in the gas phase photolysis of butene isomers at different photon energies: energy distribution in reaction products

1978 ◽  
Vol 56 (20) ◽  
pp. 2630-2637 ◽  
Author(s):  
Guy J. Collin ◽  
Andrzej Więckowski
Keyword(s):  
Quantum Yield ◽  
Kinetic Energy ◽  
Energy Distribution ◽  
Gas Phase ◽  
Excess Energy ◽  
Pressure Effects ◽  
Quantum Yields ◽  
Reaction Products ◽  
Hydrogen Atoms ◽  
Pressure Region

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 that the excess energy of the photon in the primary photoexcited butene molecules is far from being randomized before their fragmentation occurs.[Formula: see text]

THE MERCURY-PHOTOSENSITIZED DECOMPOSITION OF AMMONIA AND AMMONIA–PROPANE MIXTURES

1964 ◽  
Vol 42 (6) ◽  
pp. 1426-1432 ◽  
Author(s):  
S. Takamuku ◽  
R. A. Back
Keyword(s):  
Quantum Yield ◽  
Temperature Dependence ◽  
Primary Decomposition ◽  
Hydrogen Atoms ◽  
Increasing Temperature

A study of the mercury-photosensitized decomposition of ammonia, both with pure ammonia and with propane added as a scavenger for hydrogen atoms, suggests that the quantum yield of the primary decomposition into H and NH2 is much less than unity at 33 °C and rises with increasing temperature. The interaction of ammonia–propane mixtures with Hg 6(3P1) atoms cannot be explained in terms of simple competitive quenching; a tentative mechanism involving a long-lived Hg 6(3P1) – propane complex and Hg 6(3P0) atoms has been suggested. A temperature dependence in the relative quenching rates of C3H8 and C3D8 has also been observed.

scholarly journals The Formation of Hydrocarbons and Iron-Hydrides on Cold Interstellar Grains-Experimental Studies

1980 ◽  
Vol 87 ◽  
pp. 367-371
Author(s):  
A. Bar-Nun ◽  
M. Litman ◽  
M. Pasternak ◽  
M. L. Rappaport
Keyword(s):  
Gas Phase ◽  
Molecular Hydrogen ◽  
Experimental Studies ◽  
Carbonaceous Chondrites ◽  
Hydrogen Atoms ◽  
Mössbauer Studies ◽  
Interstellar Grains ◽  
Cold Iron

Cold hydrogen atoms at T ≥ 7K were shown experimentally to react with graphite grains at the same temperature to produce CH4 and smaller amounts of C2H6, C2H4 and C2H2. At T < 20K the hydrocarbon mantle could polymerize to form carbonaceous substances, similar to those found in carbonaceous chondrites. Further encounters with H-atoms would result in their recombination on the hydrocarbon mantle around the grains. At higher grain temperatures, the hydrocarbons formed could be ejected into the gas phase.Cold iron atoms at T < 5K were shown experimentally to react with molecular hydrogen in a T < 5K matrix. Mössbauer studies with 57Fe demonstrated the formation of an Fe-H2 bond. FeH2 and FeH molecules could be formed on grains by encounters of iron atoms with either H-atoms or H2 molecules.

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