2465-56-7Relevant articles and documents
Lin
, p. 442 (1975)
Removal Rate Constants for Singlet Methylene with Oxygen-Containing Organic Species
Gutsche, Greg J.,Lawrance, Warren D.,Staker, Warren S.,King, Keith D.
, p. 11867 - 11874 (1995)
The technique of laser flash photolysis/laser absorption has been used to obtain absolute removal rate constants for singlet methylene, 1CH2 ( 1A1) with various oxygen-containing organic species.Removal rate constants for some 27 alcohols, ethers, ketones, aldehydes, carboxylic acids, and esters are reported for the first time.The removal rate constants for H2O and CH3OH have been remeasured and found to be in excellent agreement with values determined by other researchers.Improved removal rate constants for C2H5OH, n-C3H7OH, CH3OCH3, CH3CHO, CH3COCH3, CH3COOH, HCOOCH3, and CH3OCOOCH3 are also presented.In all cases the removal rate constants are large, indicating that reaction is the dominant process leading to loss of 1CH2.Comparisons are drawn between the reactivities of the various functional groups and between them and their hydrocarbon analogues.Because of the large data base provided by these measurements, mechanistic information can be inferred in a number of instances.
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Ross,Kistiakowsky
, p. 1112 (1934)
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RATE-CONSTANTS FOR REMOVAL OF METHYLENE (1B1) PREPARED IN THE (0,13,0), (0,14,0) AND (0,18,0) OVERTONES BY HELIUM AND SEVERAL HYDROCARBONS
Castillejo, M.,Figuera, J. M.,Garcia-Moreno, I.,Medina, J. J.,Rodriguez, J. C.
, p. 597 - 601 (1990)
Methylene (1B1) was prepared by a two-step process: photodissociation of ketene at 308 nm (XeCl excimer laser) gave "cold" methylene 1A1 and CO .Subsequent excitation of the 1A1 electronic state using a dye laser produced the 1B1 state .Bending overtones v2 = 13, 14 and 18 could be selected and their time resolved fluorescence studied in the presence of several gases.Very little dependence of overtone radiative lifetimes are found.Quenching rate constants are in all cases very fast, they range from 5*10-11 cm3 molec-1 s-1 for quenching of overtone v2 = 14 by helium to 1.1*10-9 cm3 molec-1 s-1 for quenching of the same overtone by trans-2-butene.Chemical forces seem to be involved in the quenching by hydrocarbons.
Hase et al.
, p. 459,461, 462, 464-466 (1972)
Hase,Simons
, p. 4004 (1970)
Johnson et al.
, p. 3911 (1970)
Richardson,Simons
, p. 168 (1976)
Branching ratio of the C2H2 + O reaction at 290 K from kinetic modelling of relative methylene concentration versus time profiles in C2H2/O/H systems
Peeters,Boullart,Langhans
, p. 869 - 886 (1994)
In earlier work on the room temperature oxidation of C2H2 by O atoms, two distinct sources of methylene radicals have been identified: (i) direct, primary production via channel 1b of the C2H2 + O reaction, and (ii) delayed formation via the secondary reaction 3 involving the products HCCO and H of the other primary channel 1a. Presently, it was confirmed by a detailed sensitivity analysis that the precise shapes of the resulting total methylene concentration-versus-time profiles in C2H2/O systems depend strongly on the k1a/k1b branching ratio. Along that line, the important parameter k1a/k1b was determined from relative CH2 concentration-versus-time profiles measured in a variety of C2H2/O/H systems using Discharge Flow-Molecular Beam sampling Mass Spectrometry techniques (DF-MBMS). The data analysis was carried out by deductive kinetic modelling; the method, as applied to profile shapes, is discussed at length. Via this novel, independent approach, the CH2(3B1) yield of the two-channel C2H2 + O reaction was determined to be k1b/k1 = 0.17 ± 0.08. The indicated 2σ error includes possible systematic errors due to uncertainties in the rate constants of other reactions that influence the shapes of the CH2 profiles. The present result, which translates to an HCCO yield k1a/k1 = 0.83 ± 0.08, is in excellent agreement with other recent determinations. The above mechanism, with the subsequent reactions that it initiates, also reproduces the measured absolute [C2H2], [O], and [H] profiles with an average accuracy of 5%, thus validating the consistency of the C2H2/O/H reaction model put forward here.
Spectroscopic Observation of the CH2(1A1) Radical in the Reaction of C2H2 with O Atoms
Peeters, J.,Vanhaelemeersch, S.,Hoeymissen, J. Van,Borms, R.,Vermeylen, D.
, p. 3892 - 3894 (1989)
Direct spectroscopic observation of the CH2(a1A1) radical in C2H2/O/H systems (T = 295 K) is reported for the first time.Characteristic rotational features of the 1B1(0,14,0) 1A1(0,0,0)
Femtosecond dynamics of photoinduced molecular detachment from halogenated alkanes. II. Asynchronous concerted elimination of I2 from CH2I2
Zhang, Qingguo,Marvet, Una,Dantus, Marcos
, p. 4428 - 4442 (1998)
The photoinduced molecular detachment dynamics of CH2I2 have been investigated with femtosecond time resolution. Upon multiphoton excitation of CH2I2 with 312 nm femtosecond pulses, weak fluorescence in the 260-290 nm region was observed in addition to the I2 fluorescence in the 290-345 nm region studied in the previous paper. The weak fluorescence has also been interpreted as due to emission from I2, where I2 was produced from the photodissociation process CH2I2→CH2+I2*. In order to investigate the detailed dynamics of this reaction, femtosecond time-resolved data have been obtained by selective detection of the I2 fluorescence at 272 and 285 nm. From these transients, it has been found that the dissociation process takes place within the temporal width (50 fs) of the laser pulse and that the I2 photofragments exhibit coherent vibrational motion. The 272 nm transients also exhibit clear, fast decaying rotational anisotropy, quantitative analysis of which reveals a distribution of rather high rotational levels of I2. This permits us to conclude that the I2 detachment is an asynchronous concerted process; while breaking of the two CI bonds and formation of the II bond happen in a single kinetic step, one of the CI bonds breaks faster than the other. In addition, energy partitioning between the CH2 and I2 photofragments has also been explored based on the experimental observations. Since this study involves a multiphoton transition, a theoretical formulation for the time dependent rotational anisotropy is presented for the general case of multiphoton pump and multiphoton probe transitions.
Photodissociation of propyne and allene at 193 nm with vacuum ultraviolet detection of the products
Ni, Chi-Kung,Huang,Chen, Yit Tsong,Kung,Jackson
, p. 3320 - 3325 (1999)
Vacuum ultraviolet (VUV) laser photoionization is combined with time-of-flight (TOF) mass spectrometry to determine the photofragments produced from the laser photodissociation of allene and propyne in a molecular beam. Detection of C3H+3 confirms that atomic hydrogen elimination is the primary process for both of these molecules. A hydrogen molecule elimination channel and a low mass carbon fragmentation channel of allene to produce C3H2+H2 and CH2+C2H2, respectively, have also been identified. Different ratios of various dissociation channels from these two molecules suggest that the dissociation mechanisms of these two isomers are different. Dissociation must occur before complete isomerization. These results are discussed in terms of recent theoretical calculations on the ground and excited states of these molecules. Secondary photodissociation of the products has been observed, even though the laser energies that have been used are less than 8 mJ/cm2 and the photolysis laser is not focused. Therefore, the present results show how important it is to determine product distributions as a function of the laser energy.
Laufer,Bass
, p. 1635,1636, 1637 (1975)
Photodissociation dynamics of the methyl radical 3s Rydberg state
North, Simon W.,Blank, David A.,Chu, Pamela M.,Lee, Yuan T.
, p. 792 - 798 (1995)
The photodissociation dynamics of methyl radical have been investigated at 193.3 nm using photofragment translational spectroscopy.The formation of CH2 and H(2S) was the only dissociation pathway observed.Although it is not possible to assign the spin state of the methylene unambiguously, we believe the methylene is produced predominately in the 1A1 excited state.The translational energy distribution of the products is peaked at ca. 13 kcal/mole which is consistent with the magnitude of the exit barrier on the excited state potential energy surface.The breadth of the distribution suggests that the methyl radicals dissociate from a wide range of geometries.From the photofragment angular distribution an anisotropy parameter of β = -0.9+/-0.1 was determined.
Direct formation of CH2 (b 1B1) in the near-UV photodissociation of diazirine
Lim, Soon-Mi,Kim, Taek-Soo,Lim, Goo-Il,Kim, Sang Kyu,Choi, Young S.
, p. 828 - 832 (1998)
A prompt, long-lived, and red fluorescence has been observed in the photodissociation of the jet-cooled diazirine (H2CN2) excited at the origin (322.96 nm) of the S1←S0 transition. The fluorescence decays (~16 μs) and range (>575 nm) indicate that the emitting species is the electronically excited singlet methylene, CH2 (b 1B1). The linear dependence of the fluorescence intensity on the photolysis laser power strongly supports that the fluorescing CH2 (b 1B1) is produced directly from the first excited singlet state of diazirine. The observation that the fluorescence appears in the visible wavelength region indicates that the CH2 (b 1B1) fragments are highly vibrationally excited.
Gas-phase reactions of rhenium-oxo species ReOn+, n = 0, 2 6, 8, with O2, N2O, CO, H2O, H2, CH4 and C2H4
Beyer,Berg,Bondybey
, p. 1840 - 1847 (2001)
The reactions of ReOn+, n = 0, 2-6, 8, with the small molecules O2, N2O, CO, H2O, H2, CH4 and C2H4, are studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry under single collision conditions on the timescale of seconds. The ReOn+ species are produced by laser vaporization of solid rhenium and pulsed supersonic expansion in a helium-oxygen mixture into high vacuum. A wide variety of reactions are observed, including methane activation and epoxidation reactions. Re+ reacts with ethylene by sequential dehydrogenation. ReO2+ and ReO4+ exhibit the most diverse reaction pathways, while ReO5+ almost exclusively undergoes ligand exchange. ReO6+ and ReO8+ are largely unreactive, the only efficient reactions are observed are with ethylene and water. Both molecules seem to be able to directly attack the dioxygen ligands. The observed chemistry is governed by a fine interplay between available coordination sites and thermochemistry.
Koob
, p. 9,10, 11, 12 (1972)
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Rice,Glasebrook
, (1934)
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Bell,Kistiakowosky
, p. 3417 (1962)
Bernheim et al.
, p. 1280 (1970)
Frey,Walsh
, p. 158,159 (1969)
Femtosecond dynamics of photoinduced molecular detachment from halogenated alkanes. I. Transition state dynamics and product channel coherence
Marvet, Una,Zhang, Qingguo,Brown, Emily J.,Dantus, Marcos
, p. 4415 - 4427 (1998)
The direct observation of the photoinduced molecular detachment of halogens X2 from halogenated alkanes RCHX2 is presented. Three-photon excitation at 312 nm produces molecular halogens and a carbene; the halogen products are formed predominantly in the D′ state. Femtosecond pump-probe spectroscopy of the reaction reveals a fast (τa prompt dissociation without intermediates. The experimental results demonstrate vibrational coherence in the halogen product, which requires that the reaction proceed by a concerted mechanism.
The Ketyl Radical in the Oxidation of Ethyne by Atomic Oxygen at 300-600 K
Vinckier, C.,Schaekers, M.,Peeters, J.
, p. 508 - 512 (1985)
The reaction of ethyne with atomic oxygen was investigated in the temperature range 300-600 K, at a pressure of 2 torr.With molecular beam mass spectrometry, both methylene and ketyl radical were shown to be important primary products.An absolute measurement was made of the rate constant of reaction 7 of HCCO with O at T = 535 K: k7 = (1.10 +/- 0.10) X 1014 cm3 mol-1 s-1.The activation energy E7 was found to be E7 = 0.6 +/- 0.3 kcal mol-1.Reaction 2 of HCCO with H atoms is even faster; in Stern-Volmer experiments the ratio k2/k7 was determined to be 1.4 +/- 0.4 at T = 535 K and 1.3 +/- 0.2 at T = 285 K.
Experimental and modeling study of shock-tube oxidation of acetylene
Eiteneer, Boris,Frenklach, Michael
, p. 391 - 414 (2007/10/03)
Nine mixtures of acetylene and oxygen diluted in argon were studied behind reflected shock waves at temperatures of 1150-2132 K and pressures of 0.9-1.9 atm. Initial compositions were varied from very fuel-lean to moderately fuel-rich, covering equivalence ratios of 0.0625-1.66. Two more mixtures with added ethylene were used to boost the sensitivity to reactions of vinyl oxidation. The progress of reaction was monitored by laser absorption of CO molecules. The collected experimental data were subjected to extensive detailed chemical kinetics analysis. The initial kinetic model was assembled based on recent literature data and then optimized using the solution mapping technique. The analysis was extended to include recent experimental observations of Hidaka and co-workers (Combust Flame 1996, 107, 401). The derived model reproduces closely both sets of experimental data, the result obtained by modifying nine rate coefficients and three enthalpies of formation of intermediate species. The identified parameter tradeoffs and justification for the changes are discussed.
Investigation of the thermal decomposition of ketene and of the reaction CH2 + H2 ? CH3 + H
Friedrichs, Gernot,Wagner, Heinz Gg.
, p. 1601 - 1623 (2007/10/03)
Using frequency modulation (FM) spectroscopy singlet methylene radicals have been detected for the first time behind shock waves. The thermal decomposition of ketene served as source for metylene radicals at temperatures from 1905 to 2780 K and pressures around 450 mbar. For the unimolecular decomposition reaction, (1) CH2CO+M → CH2 +CO+M, the rate constants obtained are: k1 = (9.5±5.7) · 1015 · exp[(-244±25) kJ mol-1/RT] cm3mol-1 s-1. As a first study of a methylene reaction at high temperatures by diretly tracing methylene the reaction of methylene with hydrogen, (8+9) 1.3CH2 + H2 → CH3 + H, was investigated at temperatures from 1930 to 2455 K and pressures around 500 mbar. For the total rate constant of the singlet and triplet methylene reaction a temperature independent value was obtained: log(kg+9/(cm3mol-1s-1)) = 13.89±0.26. A comparison with low temperature literature data and the systematics of activation energies of triplet methylene reactions allowed a consistent description of singlet and triplet contributions and of the forward and reverse reaction. by Oldenbourg Wissenschaftsverlag, Muenchen.
