An FTIR spectroscopic study of the reactions Br + CH3CHO → HBr + CH3CO and CH3C(O)OO + NO2 ⇌ CH3C(O)OONO2 (PAN)

Based on an FTIR-product study of the photolysis of mixtures containing Br₂? CH₃CHO and Br₂? CH₃CHO? HCHO in 700 torr of N₂, the rate constant for the reaction Br + CH₃CHO → HBr + CH₃CO was determined to be 3.7 × 10^?12 cm³ molecule^?1 s^?1. In addition, the selective photochemical generation of Br at λ > 400 nm in mixtures containing Br₂? CH₃CHO? ¹⁴NO₂ (or ¹⁵NO₂)? O₂ was shown to serve as a quantitative preparation method for the corresponding nitrogen-isotope labeled CH₃C(O)OONO₂ (PAN). From the dark-decay rates of ¹⁵N-labeled PAN in large excess ¹⁴NO₂, the rate constant for the unimolecular reaction CH₃C(O)OO¹⁵NO₂ → CH₃C(O)OO + ¹⁵NO₂ was measured to be 3.3 (±0.2) × 10^?4 s^?1 at 297 ± 0.5 K.     

Kinetics of the reactions of Cl atoms with CH3Br and CH2Br2

The rate coefficients for the reactions of Cl atoms with CH₃Br, (k₁) and CH₂Br₂, (k₂) were measured as functions of temperature by generating Cl atoms via 308 nm laser photolysis of Cl₂ and measuring their temporal profiles via resonance fluorescence detection. The measured rate coefficients were: k₁ = (1.55 ± 0.18) × 10^?11 exp{(?1070 ± 50)/T} and k₂ = (6.37 ± 0.55) × 10^?12 exp{(?810 ± 50)/T} cm³ molecule^?1 s^?1. The possible interference of the reaction of CH₂Br product with Cl₂ in the measurement of k₁ was assessed from the temporal profiles of Cl at high concentrations of Cl₂ at 298 K. The rate coefficient at 298 K for the CH₂Br + Cl₂ reaction was derived to be (5.36 ± 0.56) × 10^?13 cm³ molecule^?1 s^?1. Based on the values of k₁ and k₂, it is deduced that global atmospheric lifetimes for CH₃Br and CH₂Br₂ are unlikely to be affected by loss via reaction with Cl atoms. In the marine boundary layer, the loss via reaction (1) may be significant if the Cl concentrations are high. If found to be true, the contribution from oceans to the overall CH₃Br budget may be less than what is currently assumed. © 1994 John Wiley & Sons, Inc.     

Rate coefficients for the reaction of the acetyl radical,CH3CO,with Cl2 between 253 and 384 K

Rate coefficients, k, for the gas‐phase reaction CH₃CO + Cl₂ → products (2) were measured between 253 and 384 K at 55–200 Torr (He). Rate coefficients were measured under pseudo‐first‐order conditions in CH₃CO with CH₃CO produced by the 248‐nm pulsed‐laser photolysis of acetone, CH₃C(O)CH₃, or 2,3‐butadione, CH₃C(O)C(O)CH₃. The loss of CH₃CO was monitored by cavity ring‐down spectroscopy (CRDS) at 532 nm. Rate coefficients were determined by first‐order kinetic analysis of the CH₃CO temporal profiles for [Cl₂] < 1 × 10¹⁴ molecule cm^?3 and the analysis of the CRDS profiles by the simultaneous kinetics and ring‐down method for experiments performed with [Cl₂] > 1 × 10¹⁴ molecule cm^?3. k₂(T) was found to be independent of pressure, with k₂(296 K) = (3.0 ± 0.5) × 10^?11 cm³ molecule^?1 s^?1. k₂(T) showed a weak negative temperature dependence that is well reproduced by the Arrhenius expression k₂(T) = (2.2 ± 0.8) × 10^?11 exp[(85 ± 120)/T] cm³ molecule^?1 s^?1. The quoted uncertainties in k₂(T) are at the 2σ level (95% confidence interval) and include estimated systematic errors. A comparison of the present work with previously reported rate coefficients for the CH₃CO + Cl₂ reaction is presented. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 543–553, 2009     

Kinetics of the CH2Cl + CH3 and CHCl2 + CH3 radical-radical reactions

The CH2Cl + CH3 (1) and CHCl2 + CH3 (2) cross-radical reactions were studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants were obtained in direct real-time experiments in the temperature region 301-800 K and bath gas (helium) density (6-12) x 10(16) atom cm(-3). The observed rate constant of reaction 1 can be represented by an Arrhenius expression k1 = 3.93 x 10(-11) exp(91 K/T) cm3 molecule(-1) s(-1) (+/-25%) or as an average temperature-independent value of k1= (4.8 +/- 0.7) x 10(-11) cm3 molecule(-1) s(-1). The rate constant of reaction 2 can be expressed as k2= 1.66 x 10(-11) exp(359 K/T) cm3 molecule(-1) s(-1) (+/-25%). C2H4 and C2H3Cl were detected as the primary products of reactions 1 and 2, respectively. The experimental values of the rate constant are in reasonable agreement with the prediction based on the "geometric mean rule." A separate experimental attempt to determine the rate constants of the high-temperature CH2Cl + O2 (10) and CHCl2 + O2 (11) reaction resulted in an upper limit of 1.2 x 10(-16) cm(3) molecule(-1) s(-1) for k10 and k11 at 800 K.     

Rate constants and hydrogen isotope substitution effects in the CH3 + HCl and CH3 + Cl2 reactions

The kinetics of the CH3 + Cl2 (k2a) and CD3 + Cl2 (k2b) reactions were studied over the temperature range 188-500 K using laser photolysis-photoionization mass spectrometry. The rate constants of these reactions are independent of the bath gas pressure within the experimental range, 0.6-5.1 Torr (He). The rate constants were fitted by the modified Arrhenius expression, k2a = 1.7 x 10(-13)(T/300 K)(2.52)exp(5520 J mol(-1)/RT) and k2b = 2.9 x 10(-13)(T/300 K)(1.84)exp(4770 J mol(-1)/RT) cm(3) molecule(-1) s(-1). The results for reaction 2a are in good agreement with the previous determinations performed at and above ambient temperature. Rate constants of the CH3 + Cl2 and CD3 + Cl2 reactions obtained in this work exhibit minima at about 270-300 K. The rate constants have positive temperature dependences above the minima, and negative below. Deuterium substitution increases the rate constant, in particular at low temperatures, where the effect reaches ca. 45% at 188 K. These observations are quantitatively rationalized in terms of stationary points on a potential energy surface based on QCISD/6-311G(d,p) geometries and frequencies, combined with CCSD(T) energies extrapolated to the complete basis set limit. 1D tunneling as well as the possibility of the negative energies of the transition state are incorporated into a transition state theory analysis, an approach which also accounts for prior experiments on the CH3 + HCl system and its various deuterated isotopic substitutions [Eskola, A. J.; Seetula, J. A.; Timonen, R. S. Chem. Phys. 2006, 331, 26].     

Kinetics of the reactions of CH3O with Br and BrO at 298 K

A discharge flow reactor coupled to a laser-induced fluorescence (LIF) detector and a mass spectrometer was used to study the kinetics of the reactions CH₃O+Br→products (1) and CH₃O+BrO→products (2). From the kinetic analysis of CH₃O by LIF in the presence of an excess of Br or BrO, the following rate constants were obtained at 298 K: k₁=(7.0±0.4)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and k₂=(3.8±0.4)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The data obtained are useful for the interpretation of other laboratory studies of the reactions of CH₃O₂ with Br and BrO. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 249–255, 1998.     

Rate coefficients for the O(3P) + Cl2O gas‐phase reaction between 230 and 357 K

Rate coefficients, k, for the gas‐phase reaction of O(³P) atoms with Cl₂O (dichlorine monoxide) over a range of temperatures (230–357 K) at pressures between 12 and 32 Torr (N₂) are reported. Rate coefficients were measured under pseudo‐first‐order conditions in O(³P) using pulsed laser photolysis to produce O(³P) atoms and atomic resonance fluorescence to detect its temporal profile. The rate coefficient temperature dependence is given by the Arrhenius expression k(T) = (1.51 ± 0.20) × 10^?11 exp[?(477 ± 30)/T] cm³ molecule^?1 s^?1, and k(296 K) was measured to be (2.93 ± 0.30) × 10^?12 cm³ molecule^?1 s^?1. The quoted uncertainty limits are at the 2σ (95% confidence) level and include estimated systematic errors. The rate coefficients determined in the present study, under conditions that minimized secondary losses of O(³P), are compared with previous results from other laboratories and the discrepancies are discussed. © 2011 Wiley Peiodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America.

Int J Chem Kinet 43: 312–321, 2011     

Rate coefficients for the OH + acetaldehyde (CH3CHO) reaction between 204 and 373 K

The rate coefficient, k₁, for the gas‐phase reaction OH + CH₃CHO (acetaldehyde) → products, was measured over the temperature range 204–373 K using pulsed laser photolytic production of OH coupled with its detection via laser‐induced fluorescence. The CH₃CHO concentration was measured using Fourier transform infrared spectroscopy, UV absorption at 184.9 nm and gas flow rates. The room temperature rate coefficient and Arrhenius expression obtained are k₁(296 K) = (1.52 ± 0.15) × 10^?11 cm³ molecule^?1 s^?1 and k₁(T) = (5.32 ± 0.55) × 10^?12 exp[(315 ± 40)/T] cm³ molecule^?1 s^?1. The rate coefficient for the reaction OH (ν = 1) + CH₃CHO, k₇(T) (where k₇ is the rate coefficient for the overall removal of OH (ν = 1)), was determined over the temperature range 204–296 K and is given by k₇(T) = (3.5 ± 1.4) × 10^?12 exp[(500 ± 90)/T], where k₇(296 K) = (1.9 ± 0.6) × 10^?11 cm³ molecule^?1 s^?1. The quoted uncertainties are 2σ (95% confidence level). The preexponential term and the room temperature rate coefficient include estimated systematic errors. k₇ is slightly larger than k₁ over the range of temperatures included in this study. The results from this study were found to be in good agreement with previously reported values of k₁(T) for temperatures <298 K. An expression for k₁(T), suitable for use in atmospheric models, in the NASA/JPL and IUPAC format, was determined by combining the present results with previously reported values and was found to be k₁(298 K) = 1.5 × 10^?11 cm³ molecule^?1 s^?1, f(298 K) = 1.1, E/R = 340 K, and Δ E/R (or g) = 20 K over the temperature range relevant to the atmosphere. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 635–646, 2008     

Rate coefficients for the reactions of OH with CF3CH2CH3 (HFC-263fb), CF3CHFCH2F (HFC-245eb), and CHF2CHFCHF2 (HFC-245ea) between 238 and 375 K

Rate coefficients for reaction of the hydroxyl radical (OH) with three hydrofluorocarbons (HFCs) CF3CH2CH3, HFC-263fb, (k1); CF3CHFCH2F, HFC-245eb, (k2); and CHF2CHFCHF2, HFC-245ea, (k3); which are suggested as potential substitutes to chlorofluorocarbons (CFCs), were measured using pulsed laser photolysis-laser-induced fluorescence (PLP-LIF) between 235 and 375 K. The Arrhenius expressions obtained are k1(T) = (4.36 +/- 0.72) x 10(-12) exp[-(1290 +/- 40)/T] cm3 molecule(-1) s(-1); k2(T) = (1.23 +/- 0.18) x 10(-12) exp[-(1250 +/- 40)/T] cm3 molecule(-1) s(-1); k3(T) = (1.91 +/- 0.42) x 10(-12) exp[-(1375 +/- 100)/T] cm3 molecule(-1) s(-1). The quoted uncertainties are 95% confidence limits and include estimated systematic errors. The present results are discussed and compared with rate coefficients available in the literature. Our results are also compared with those calculated using structure activity relationships (SAR) for fluorinated compounds. The IR absorption cross-sections at room temperature for these compounds were measured over the range of 500 to 4000 cm-1. The global warming potentials (GWPs) of CF3CH2CH3(HFC-263fb), CF3CHFCH2F(HFC-245eb), and CHF2CHFCHF2(HFC-245ea) were calculated to be 234, 962, and 723 for a 20-year horizon; 70, 286, and 215 for a 100-year horizon; and 22, 89, and 68 for a 500-year horizon; and the atmospheric lifetimes of these compounds are 0.8, 2.5, and 2.6 years, respectively. It is concluded that these compounds are acceptable substitutes for CFCs in terms of their impact on Earth's climate.     

Theoretical study and rate constants calculation for the reactions X + CF3CH2OCF3 (X = F,Cl, Br)

The multiple‐channel reactions X + CF₃CH₂OCF₃ (X = F, Cl, Br) are theoretically investigated. The minimum energy paths (MEP) are calculated at the MP2/6‐31+G(d,p) level, and energetic information is further refined by the MC‐QCISD (single‐point) method. The rate constants for major reaction channels are calculated by canonical variational transition state theory (CVT) with small‐curvature tunneling (SCT) correction over the temperature range 200–2000 K. The theoretical three‐parameter expressions for the three channels k_1a(T) = 1.24 × 10^?15T^1.24exp(?304.81/T), k_2a(T) = 7.27 × 10^?15T^0.37exp(?630.69/T), and k_3a(T) = 2.84 × 10^?19T^2.51 exp(?2725.17/T) cm³ molecule^?1 s^?1 are given. Our calculations indicate that hydrogen abstraction channel is only feasible channel due to the smaller barrier height among five channels considered. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2012     

Anion-controlled redistribution reactions in the system C3Cl3+A−/(CH3)3SiN(CH3)2

Transmination reactions of the 4z-exchange type between C₃Cl₃⁺A^? and (CH₃)₃SiN(CH₃)₂ are introduced as a novel mode of aromatic substitution at the C₃⁺-core. The extent of transamination can be controlled by appropriate choice of counterion A^?.     

Nonadiabatic dynamics in the CH3+HCl-->CH4+Cl(2PJ) reaction

Nonadiabatic dynamics in the title reaction have been investigated by 2+1 REMPI detection of the Cl(2P(3/2)) and Cl*(2P(1/2)) products. Reaction was initiated by photodissociation of CH(3)I at 266 nm within a single expansion of a dilute mixture of CH(3)I and HCl in argon, giving a mean collision energy of 7800 cm(-1) in the center-of-mass frame. Significant production of Cl* was observed, with careful checks made to ensure that no additional photochemical or inelastic scattering sources of Cl* perturbed the measurements. The fraction of the total yield of Cl(2P(J)) atoms formed in the J=1/2 level at this collision energy was 0.150+/-0.024, and must arise from nonadiabatic dynamics because the ground potential energy surface correlates to CH(4)+Cl(2P(3/2)) products.     

Rate coefficients for the gas‐phase reactions of OH radicals with methylbutenols at 298 K

The relative‐rate method has been used to determine the rate coefficients for the reactions of OH radicals with three C₅ biogenic alcohols, 2‐methyl‐3‐buten‐2‐ol (k₁), 3‐methyl‐3‐buten‐1‐ol (k₂), and 3‐methyl‐2‐buten‐1‐ol (k₃), in the gas phase. OH radicals were produced by the photolysis of CH₃ONO in the presence of NO. Di‐n‐butyl ether and propene were used as the reference compounds. The absolute rate coefficients obtained with the two reference compounds agreed well with each other. The O₃ and O‐atom reactions with the target alcohols were confirmed to have a negligible contribution to their total losses by using two kinds of light sources with different relative rates of CH₃ONO and NO₂ photolysis. The absolute rate coefficients were obtained as the weighted mean values for the two reference compound systems and were k₁ = (6.6 ± 0.5) × 10^?11, k₂ = (9.7 ± 0.7) × 10^?11, and k₃ = (1.5 ± 0.1) × 10^?10 cm³ molecule^?1 s^?1 at 298 ± 2 K and 760 torr of air. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 379–385 2004     

Rate constants for the reactions of molecular iodine with Cl,SiCl3, and SiH3 at 298 K

Rate constants k₁, k₂, and k₃ have been measured at 298 K by means of a laser photolysis-laser magnetic resonance technique and (or) by a laser photolysis-infrared chemiluminescence detection technique (LMR and IRCL, respectively). \hfill\hbox to 12em{$\rm Cl+I_2\longrightarrow ICl+I;$}\hbox to 8em{$\rm {\it k}_1=(2.5\pm 0.7)\times 10^{-10}(IRCL)$}\hfill(1)\\\hfill\hbox to 12em{}\hbox to 8em{$\rm {\it k}_1=(2.8\pm 0.8)\times 10^{-10}(LMR)$}\hfill \\\hfill\hbox to 12em{$\rm SiCl_3+I_2\longrightarrow SiCl_3I+I;$}\hbox to 8em{$\rm {\it k}_2=(5.8\pm 1.8)\times 10^{-10}(IRCL)$}\hfill (2)\\\hfill\hbox to 12em{$\rm SiH_3+I_2\longrightarrow SiIH_3+I;$}\hbox to 8em{$\rm {\it k}_3=(1.8\pm 0.46)\times 10^{-10}(LMR)$}\hfill (3)\\ As an average of the LMR and IRCL results we offer the value k₁ = (2.7 ± 0.6) × 10⁻¹⁰. Units are cm³ molecule⁻¹ s⁻¹; uncertainties are 2σ including precision and estimated systematic errors. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 25–33, 1997.     

The very-low-pressure study of the kinetics and equilibrium: Cl + CH4 ⇄ CH3 + HCl at 298 K. The heat of formation of the CH3 radical

The bimolecular rate constant for the direct reaction of chlorine atoms with methane was measured at 25°C by using the very-low-pressure-pyrolysis technique. The rate constant was found to be In addition, the ratio k₁/k_?1 was observed with about 25% accuracy: K₁₍₂₉₈₎ = 1.3 ± 0.3. This gives a heat of formation of the methyl radical ΔH° _{f 298}(CH₃) = 35.1 ± 0.15 kcal/mol. A bond dissociation energy BDE (CH₃ ? H) = 105.1 ± 0.15 kcal/mol in good agreement with literature values was obtained.     

Chemical reactions inside structured nano-environment: S(N)2 vs. E2 reactions for the F(-) + CH(3)CH(2)Cl system

A new receptor for S(N)2 transition states, named NPTROL, is proposed. This molecule has a cavity and four hydroxyl groups that are able to interact with ionic S(N)2 and E2 transition states. Its catalytic effect and selectivity was investigated through high level ab initio calculations using the fluoride ion plus ethyl chloride in DMSO solution as a model system. Calculations at the ONIOM[CCSD(T)/6-311+G(2df,2p)?:?MP2/BASIS1] level of theory and solvent effects, included through a continuum solvation model, indicate that NPTROL is able to catalyze the S(N)2 pathway and has an inverse effect on the E2 pathway. Inside the NPTROL cavity, the ΔG(?) for the S(N)2 transition state is 5.00 kcal mol(-1) lower than that for E2, and as a consequence this reaction becomes highly selective toward the S(N)2 product.     

Schwingungsspektren und Kraftkonstanten der Übergangsreihen OP(N(CH3)2)3 – OP(CH3)3 und SP(N(CH3)2)3 – SP(CH3)3

Vibrational Spectra and Force Constants of the Series OP(N(CH₃)₂)₃ – OP(CH₃)₃ and SP(N(CH₃)₂)₃ – SP(CH₃)₃ The vibrational spectra (IR and Raman) of the compounds of the title series are recorded and assigned to the normal vibrations. By a simplified force field the valence force constants are calculated and discussed. The results are compared with those of the NMR spectroscopy.     

Rate coefficients for the OH + CFH2CH2OH reaction between 238 and 355 K

The rate coefficient for the reaction OH + CFH2CH2OH --> products (k1) between 238 and 355 K was measured using the pulsed laser photolysis-laser induced fluorescence (PLP-LIF) technique to be (5.15 +/- 0.88)x 10(-12) exp[-(330 +/- 45)/T] cm3 molecule(-1) s(-1); k1(298 K)= 1.70 x 10(-12) cm3 molecule(-1) s(-1). The quoted uncertainties are 2sigma(95% confidence level) and include estimated systematic errors. The present results are discussed in relation to the measured rate coefficients for the reaction of OH with other fluorinated alcohols and those calculated using recently reported structure additivity relationships for fluorinated compounds (K. Tokuhashi, H. Nagai, A. Takahashi, M. Kaise, S. Kondo, A. Sekiya, M. Takahashi, Y. Gotoh and A. Suga, J. Phys. Chem. A, 1999, 103, 2664-2672, ). Infrared absorption cross sections for CFH2CH2OH are reported and they are used to calculate the global warming potentials (GWP) for CFH2CH2OH of approximately 8, approximately 2, and approximately 1, respectively, for the 20, 100 and 500 year horizons. A brief discussion of the atmospheric degradation of CFH2CH2OH is provided. It is concluded that CFH2CH2OH is an acceptable substitute for CFCs in terms of its impact on Earth's climate and the composition of the atmosphere. The room temperature rate coefficient for the reaction OH + CFH2CH2OH --> products (k10) was measured to be 3.26 x 10(-12) cm3 molecule(-1) s(-1), in good agreement with recent measurements from this laboratory.