Experimental Kinetics Study of the Reaction of Boron Atoms, B( 2 P J ), with Ethylene at Very Low Temperatures (23−295 K) (original) (raw)
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Physical Chemistry Chemical Physics, 2004
The reaction dynamics of atomic boron, B(2 P), with acetylene, C 2 H 2 (X 1 S g þ), were investigated at two collision energies of 12.9 kJ mol À1 and 16.3 kJ mol À1 employing the crossed molecular beams technique. Only the atomic boron versus hydrogen atom exchange pathway was observed. Forward-convolution fitting of the laboratory data at m/z ¼ 36 (11 BC 2 H þ) shows that the reaction dynamics are indirect, proceed via addition of the boron atom to the carbon-carbon triple bond via a cyclic intermediate, and form the linear HBCC(X 1 S þ) molecule after an atomic hydrogen ejection. The formation of the HBCC(X 1 S þ) isomer under single collision conditions presents the first '' clean '' gas phase synthesis of this important organo-boron molecule and opens the door to a prospective spectroscopic investigation.
Journal of the American Chemical Society, 1994
Pulsed-laser ablated B atoms react with Hz upon condensation with excess argon to give BH, a (Hz)(BH) complex, and B2H6 as the major products. The initial reaction to form BH requires activation energy, and BH reacts with Hz to give additional products. Sharp new bands at 2587.3 and 1129.2 cm-I exhibit natural isotopic 1:4 doublets for vibrations involving a single boron atom and disappear on annealing to 25 K. Substitution of 1OB and D gives shifts that are matched by MBPT(2) calculations of vibrational spectra for planar BH3. Broader bands at 2475.2 and 1134.3 cm-1 exhibit similar isotopic shifts for vibrations of a BH3 submolecule and decrease on annealing to 25 K. The displacements from isolated BH3 frequencies suggest a (Hz)(BHs) complex and are in general agreement with recent quantumchemical calculations for BHs. A sharp 2679.9-cm-1 band gives the IOB shift predicted by MBPT(2) calculations for linear HBBH. A weak 2212.8-cm-l band exhibits the 1OB shift and frequency calculated for the strongest band of BH4-. Additional broad absorptions that remain on annealing are attributed to higher boranes.
Journal of Physical Chemistry A, 1999
Reactions of methyl radicals with hydrogen bromide CH 3 + HBr f CH 4 + Br (1) and bromine atoms CH 3 + Br f CH 3 Br (2) were studied using excimer laser photolysis-transient UV spectroscopy at 297 ( 3 K over the 1-100 bar buffer gas (He) pressure range. Methyl radicals were produced by 193 nm (ArF) laser photolysis of acetone, (CH 3 ) 2 CO, and methyl bromide, CH 3 Br. Temporal profiles of methyl radicals were monitored by UV absorption at 216.51 nm (copper hollow cathode lamp with current boosting). The yield of acetyl radicals in photolysis of acetone at 193 nm was found to be less than 5% at 100 bar He based on the transient absorptions at 222.57 and 224.42 nm. The measured rate constants for reaction 1 are k 1 ) (2.9 ( 0.7) × 10 -12 , (3.8 ( 1.5) × 10 -12 , and (3.4 ( 1.3) × 10 -12 cm 3 molecule -1 s -1 at the buffer gas (He) pressures of 1.05, 11.2, and 101 bar, respectively. The rate data obtained in this study confirmed high values of the previous (low pressure) measurements and ruled out the possibility of interference of excited species. The measured rate constant is independent of pressure within the experimental error. The rate constant of reaction of methyl radicals with bromine atoms (2) was determined relative to the rate constant of methyl radical self-reaction, CH 3 + CH 3 f C 2 H 6 (3) in experiments with photolysis of CH 3 Br: k 2 /k 3 ) 0.92 ( 0.32, 1.15 ( 0.30, and 1.65 ( 0.26 at 1.05, 11.2, and 101 bar He, respectively. On the basis of the literature data for reaction 3, this yields k 2
Chemical Physics Letters, 2004
The first study of the kinetics of B atoms with O 2 at low and ultra-low temperatures is reported. Rate constants have been measured from 295 down to 24 K using the pulsed-laser photolysis-laser-induced fluorescence technique in a Cin etique de R eaction en Ecoulement Supersonique Uniforme apparatus. Rate constants were found to increase monotonically with decreasing temperature. The temperature dependence of the rate constant has also been calculated using a theoretical approach based on the adiabatic capture centrifugal sudden approximation method. In the limit of zero temperature, the reactivities of the two spin orbit states of the B atom towards the O 2 molecule are also demonstrated to be different.
Boron chemistry in a new light
Chemical Science, 2015
Activation of stable boron species with visible-light allows the creation of boryl and/or carbon radicals through single electron- or energy transfer.
Journal of Physical Chemistry A, 2008
The rate constants for the reactions of atomic bromine with dimethyl ether and diethyl ether were measured from approximately 300 to 350 K using the relative rate method. Both isooctane and isobutane were used as the reference reactants, and the rate constants for the reactions of these hydrocarbons were measured relative to each other over the same temperature range. The kinetic measurements were made by photolysis of dilute mixtures of bromine, the reference reactant, and the test reactant in mixtures of argon and oxygen at a total pressure of 1 atm. The resulting ratios of rate constants were combined with the absolute rate constant as a function of temperature for the reference reaction of Br with isobutane to calculate absolute rate constants for the reactions of Br with isooctane, dimethyl ether, and diethyl ether. The absolute rate constant, in the units cm 3 molecule-1 s-1 , for the reaction of Br with dimethyl ether was given by k) (3.8 (2.4) × 10-10 exp-(-(3.54 (0.21) × 10 3 /T) while for the reaction of Br with diethyl ether the rate constant is given by k) (2.8 (2.7) × 10-10 exp(-(2.44 (0.32) × 10 3 /T). On the same basis, the rate constant for the reaction of Br with isooctane is given by k) (3.34 (0.59) × 10-12 exp(-(1.80 (0.11) × 10 3 /T). In each case, the activation energy of the reaction is significantly smaller than the endothermicity of the reaction. This is discussed in terms of a complex mechanism for these reactions.
The Journal of Physical Chemistry A, 2006
Kinetics of the reaction Br + CH 2 ClBr T CHClBr + HBr (1,-1) were studied experimentally in the forward direction. The absolute reaction kinetics method of laser flash photolysis coupled with Br atom resonance fluorescence detection and three different relative-rate methods with gas-chromatographic analysis were applied to carry out the experiments. The rate constants determined were found to obey the Arrhenius law in the wide temperature range of T) 293-785 K providing the kinetic expression k 1) (2.8 (0.1) × 10 13 exp[-(47.6 (0.3) kJ mol-1 /RT] cm 3 mol-1 s-1 (the errors given refer to 1σ precision). An ab initio direct dynamics method was used to study reaction (1,-1) theoretically. The electronic structure information including geometries, gradients, and force constants was obtained at the MP2 level of theory; and energies were improved at higher theoretical levels. Rate constants were calculated using the canonical variational transition state theory with small-curvature tunneling correction over the temperature range 200-1000 K. Theory substantially underestimates k 1 compared to experiment. The agreement was found good with k-1 reported previously predicting positive temperature dependence. The experimental kinetic parameters were utilized in thermochemical calculations yielding the recommended standard enthalpy of formation of ∆ f H°2 98 (CHClBr)) (140 (4) kJ mol-1 (with 2σ accuracy given).
Chemical Physics Letters, 2005
A kinetic mechanism was developed for the growth of boron nitride films, including up to 35 species and 1012 gas-phase reactions. For 117 elementary reactions, rate constants are available from published experimental/theoretical data and a code was written to estimate the others using transition state theory. As an example of our approach, we report here results for one of these reactions, BF 2 + NF = BF 3 + N of presumable importance for the mechanism, using geometries and electronic energies (including their first and second derivatives), calculated ab initio along the minimum energy path. The reaction proceeds in two steps and rate constants were calculated for the temperature range 200-4000 K.
Kinetics of the reactions of bromine atoms with a series of aliphatic aldehydes at 298 K
1998
The kinetics of the reactions of B~f ' p~~) with selected aldehydes, i.e. ethanal (l), propanal (2). 2-methyl-propanal (3), 2,2-dhethyl-propanal (4) and trichloroacetaldehyde (5) were studied at 298*2 K. Rate constants for overall reactions were measured using the fast flow technique with resonance fluorescence detection of Br. Complementary determinations were carried out by the laser flash photolysis method. The following rate constants were obtained in the kinetic measurements (220): kl=(2.1i0.2)x101', k~=(4.3*0.4)X1O1', k3=(6.3+1.4)x1012, k.,=(8.5*O.8)x1O1', k5Slx109, all in cm3 m o l-'~-~ units. The probable mechanism for the reactions of bromine atoms with aliphatic aldehydes has been discussed.
Gas phase reaction kinetics in boron fibre production
AIChE Journal, 2012
in Wiley Online Library (wileyonlinelibrary.com). In the production of boron fibres using the chemical vapor deposition (CVD) technique, boron deposition and dichloroborane formation reactions occurs simultaneously. Boron deposition reaction occurs at the surface, whereas the formation of dichloroborane is the result of both gas phase and surface reactions. A continuous stirred tank reactor (CSTR) type of reactor was designed to investigate the reaction kinetics and kinetic parameters in the gas phase reactions of boron trichloride and hydrogen. It was concluded that reaction rate of the product increased with an increase in the inlet concentration of both reactants (BCl 3 and H 2) and with an increase in the reactor temperature. While reaction order with respect to BCl 3 was almost constant at about 0.5 at each temperature, reaction order with respect to hydrogen increased significantly at temperatures lower than 350 C. A general rate expression was derived for BHCl 2 formation from BCl 3 and hydrogen. V