2465-56-7Relevant academic research and scientific papers
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.
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.
Photodissociation dynamics of the CH2Cl radical: Ion imaging studies of the Cl+CH2 channel
Dribinski,Potter,Demyanenko,Reisler
, p. 7474 - 7484 (2001)
Photodissociation of the chloromethyl radical, CH2Cl to chlorine atom and methylene, which can serve as a prototype for halogenated methyl radicals, was described. Ch2Cl was produced in a molecular beam using pulsed pyrolysis. Cl and CH2 products were detected by laser ionization and their velocity and angular distributions were determined using the ion imaging technique. The available energy was partitioned into the translational degrees of freedom. It was found that the CH2Cl generated in a molecular beam via pulsed pyrolysis exhibits continuous, unstructured absorption throughout the investigated region, with Cl atoms as major products.
The correlated product state distribution of ketene photodissociation at 308 nm
Morgan, Christopher G.,Drabbels, Marcel,Wodtke, Alec M.
, p. 7460 - 7474 (1996)
The correlated product state distribution for ketene photodissociation (CH2CO→CH2+CO) at 308 nm has been measured by using quantum-state-specific metastable time-of-flight (TOF) spectroscopy. This distribution is a matrix whose elements are the probability that if CO is produced in the dissociation with quantum-state |nCO〉, CH2 will be produced with quantum-state |nCH2〉. It was found that ketene photodissociation yields CH2 in three resolved states; the 1A1(000), and 1A1(010) states of CH2 are the major channels, while the 3B1 state is a minor channel. In addition to this scalar distribution, the vector correlations between the recoil velocity and the angular momentum of the CO fragment (v·j correlation), expressed by theβ00(22) bipolar moment, have also been obtained as a function of the kinetic energy release of the photoreaction. The correlated product state distribution was found not to follow the predictions of phase space theory, suggesting that dynamic hindrances exist in the photoreaction that have not been previously observed. A phase space theory calculation with restricted impact parameter values was also performed and compared to experiment. The impact parameter restricted phase space theory more accurately reproduced all of the correlated product state information obtained in this work as well as previous uncorrelated product state distributions for CH2 and CO. Both the ranges and the values of the allowed impact parameters obtained from these restricted calculations increase as the rotational energy of CO increases. Also, the values of the allowed impact parameters for 1A1(010) CH2 are larger than for 1A1(000) CH2. This strongly suggests that C-C-O bending modes are hindered at the transition state and therefore play an important role in the photodissociation.
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.
Direct Measurement of the Reaction CH3 + OH at Ambient Temperature in the Pressure Range 0.3 - 6.2 mbar
Oser, H.,Stothard, N. D.,Humpfer, R.,Grotheer, H. H.
, p. 5359 - 5363 (1992)
The falloff behavior of the CH3 + OH recombination reaction CH3 + OH -> CH3OH (1a) has been quantitatively investigated for the first time.Methyl decay profiles were measured in a flow reactor at 300 K and in a pressure range between 0.3 and 6.2 mbar.The experimental conditions were such that a possible channel to 1CH2 + H2O did not contribute strongly to the CH3 profiles.Rate coefficients were extracted from the data by comparison of the experimental profiles with compouter simulations.The results are in accord with the limiting rate coefficient suggested by Hochanadel et al., k1a(298 K) = 9.3 * 10-11 cm3 molecule-1 s-1.The experimental falloff curve is described by use of this value for K, together with an interpolation formula given by Troe, from which an approximate value for the low-pressure limit K01a = (2.5 +/- 1.0) * 10-27 cm6 molecule-2 s-1 has been derived (bath gas helium).For a quantitative assessment of the possible channel to 1CH2 + H2O, reaction 1d measurements of H2O were carried out, yielding an estimated upper limit for the rate coefficient of K1d(300 K) -12 cm3 molecule-1 s-1.
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.
