Laser Photolysis-laser Induced Fluorescence Technique Research Articles

Laser induced fluorescence and computational studies on the tropospheric photooxidation reactions of methyl secondary butyl ether initiated by OH radicals.

The kinetics of the reaction of methyl secondary butyl ether with OH radicals was investigated experimentally using the pulsed laser photolysis-laser induced fluorescence technique (PLP-LIF) over temperatures ranging from 268 to 363K. The rate coefficient value at 298K was measured to be (1.09 ± 0.02) × 10-11 cm3 molecule-1s-1 and the deduced Arrhenius expression is [Formula: see text]= (2.21 ± 0.29) × 10-12 exp ((471.71 ± 38.50)/T) cm3 molecule-1s-1. To complement the experimental data, the kinetic study of the title reaction was performed computationally at CCSD(T)/cc-pVTZ//M06-2X/6-311 + G(d,p) level of theory with the incorporation of tunnelling correction from 200 to 400K. The end products formed were qualitatively analyzed by using gas chromatography equipped with mass spectrometry (GC-MS) as detection technique and the mechanism for degradation was proposed. Thermochemical parameters were evaluated to determine the feasibility of individual reaction pathways. Atmospheric implications were evaluated and discussed in this manuscript.

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

The kinetics of the reactions of PO with O2 and PO2 with O3 were studied at temperatures ranging from ~ 190 to 340 K, using a pulsed laser photolysis-laser induced fluorescence technique. For the reaction of PO + O2 there is evidence of both a two- and three-body exit channel, producing PO2 + O and PO3, respectively. Potential energy surfaces of both the PO + O2 and PO2 + O3 systems were calculated using electronic structure theory, and combined with RRKM calculations to explain the observed pressure and temperature dependences. For PO + O2, at pressures typical of a planetary upper atmosphere where meteoric ablation of P will occur, the reaction is effectively pressure independent with a yield of PO2 + O of > 99%; the rate coefficient can be expressed by: log10(k, 120 - 500 K, cm3 molecule-1 s-1) = -13.915 + 2.470log10(T) - 0.5020(log10(T))2, with an uncertainty of ± 10 % over the experimental temperature range (191 - 339 K). With increasing pressure, the yield of PO3 increases, reaching ~ 90% at a pressure of 1 atm and T = 300 K. For PO2 + O3, k(188 - 339 K) = 3.7 × 10-11 exp(-1131/T) cm3 molecule-1 s-1, with an uncertainty of ± 26 % over the stated temperature range. Laser induced fluorescence spectra of PO over the wavelength range of 245 - 248 nm were collected and simulated using PGOPHER to obtain new spectroscopic constants for the ground and v = 1 vibrational levels of the X2Π and A2Σ+ states of PO.

Kinetic studies of the gas phase reaction of 1,2-propylene oxide with the OH radical over a temperature range of 261–335 K

Abstract The rate coefficient for the gas phase reaction of the OH radical with 1,2-propylene oxide (PPO) has been measured at 298 K using a relative rate method, employing Gas Chromatography (GC) technique, using ethane and 1,2-dichloroethane as reference compounds. Temperature dependence of the above reaction is also studied using an absolute rate method, employing Laser Photolysis-Laser Induced Fluorescence (LP-LIF) technique, over a range of 261–335 K. The measured bimolecular rate coefficients were fitted into the Arrhenius plot, which yielded a straight line roughly parallel to the x-axis and implies no or very weak temperature dependence. Within the experimental error limits, rate coefficients obtained at various temperatures, are found to vary within a narrow range from (4.65 ± 0.24) × 10−13 to (4.80 ± 0.24) × 10−13 cm3 molecule−1 s−1. Room temperature rate coefficient of the reaction of PPO with the OH radical was found to be (4.65 ± 0.24) × 10−13 cm3 molecule−1 s−1, using LP-LIF technique. These results have been discussed with available literature to unveil the probable mechanism. An average tropospheric lifetime of PPO has been estimated to be about two weeks for degradation by the OH radical. In addition, atmospheric parameters such as Radiative Efficiency (RE) and Global Warming Potential (GWP) for PPO are determined. Stable products formed are characterized using GC-MS and FT-IR techniques. Theoretical calculations are performed to understand the energetics and mechanism of H atom abstraction by OH, and also to complement the experimental observations.

Rate coefficients of reactions of 1-chlorocyclopentene with tropospheric oxidants at 298 K

The reactions of 1-chlorocyclopentene with tropospheric oxidants, Cl, OH and O3 are studied to measure the rate coefficients at 298 K and 800 Torr of N2 using the relative rate method with butene, cyclopentene and butane as references. The concentrations of the organics are measured by Gas Chromatograpy technique. The measured average rate coefficient values of kCl, kOH and kO3 (in cm3 molecule−1 s−1) are (3.51 ± 1.26) x 10−10, (5.97 ± 1.08) x 10−11 and (1.50 ± 0.19) x 10−17, respectively. In addition, the rate coefficient for reaction of OH with 1-chlorocyclopentene at 298 K and 30 Torr was also measured using an absolute method of laser photolysis-laser induced fluorescence technique, and the kOH value is found to be (6.01 ± 0.70) x 10−11 cm3 molecule−1 s−1. The stable products formed during the reaction of Cl, OH and O3 initiated oxidation of the 1-chlorocyclopentene in presence of air are characterized by GCMS. The abstraction and addition products are identified among them, the latter are found to be major products. The experimental results are supported by molecular orbital calculations, and abstraction of the allylic hydrogen atoms is predicted to be the major abstraction channel. Calculations predict the preferential addition of chlorine atom to the carbon atom of the unsaturation center not having Cl attached to it. The rate coefficients of 1-chlorocyclopentene are compared with that of cyclopentene and substituted cyclopentene to understand the effect of substituent Cl on the reactivity. The measured rate coefficients have been used to calculate tropospheric lifetime of the compound to be 316, 2 and 26 h for Cl, OH and O3, respectively. Based on these values, the major degradation pathway of 1-chlorocyclopentene is suggested to be its reaction with OH. Atmospheric impact of these molecules is local as tropospheric lifetime (τ) < 2 h. Using the tropospheric lifetime of 1-chlorocyclopentene, and its IR absorption cross-section in tropospheric IR window and under the assumption of a well mixed atmosphere, the radiative forcing of 1-chlorocyclopentene was estimated to be 22.41 mWm−2 ppb−1, and the global warming potentials for 20 and 100 years time horizon were calculated to be 0.01 and 0.003, respectively.

Rate coefficients of hydroxyl radical reaction with dimethyl ether over a temperature range of 257–333 K

The reaction of dimethyl ether (DME) with OH radical was studied using a laser photolysis-laser induced fluorescence technique in the temperature range of 257–333 K at 30 Torr. The temperature dependent rate coefficient is represented by the expression, kT=9.7±1.0×10-12exp-380±25/Tcm3molecules-1s-1 and atmospheric lifetime was found to be 4.7 days. To elucidate the reaction mechanism and complement the experimental work, the energies and structures of the reactants and transition states involved were determined theoretically using the G3 method. The radiative forcing and the global warming potential for 100 years time horizon of DME were estimated to be 0.03 W m−2 ppb−1 and 0.02, respectively.

Temperature Dependent Rate Coefficients for the Gas-Phase Reaction of the OH Radical with Linear (L2, L3) and Cyclic (D3, D4) Permethylsiloxanes.

Permethylsiloxanes are emitted into the atmosphere during production and use as personal care products, lubricants, and cleaning agents. The predominate atmospheric loss process for permethylsiloxanes is expected to be via gas-phase reaction with the OH radical. In this study, rate coefficients, k(T), for the OH radical gas-phase reaction with the two simplest linear and cyclic permethylsiloxanes were measured using a pulsed laser photolysis-laser induced fluorescence technique over the temperature range of 240-370 K and a relative rate method at 294 K: hexamethyldisiloxane ((CH3)3SiOSi(CH3)3, L2), k1; octamethyltrisiloxane ([(CH3)3SiO]2Si(CH3)2, L3), k2; hexamethylcyclotrisiloxane ([-Si(CH3)2O-]3, D3), k3; and octamethylcyclotetrasiloxane ([-Si(CH3)2O-]4, D4), k4. The obtained k(294 K) values and temperature-dependence expressions for the 240-370 K temperature range are (cm3 molecule-1 s-1, 2σ absolute uncertainties): k1(294 K) = (1.28 ± 0.08) × 10-12, k1( T) = (1.87 ± 0.18) × 10-11 exp(-(791 ± 27)/ T); k2(294 K) = (1.72 ± 0.10) × 10-12, k2( T) = 1.96 × 10-13 (T/298)4.34 exp(657/ T); k3(294 K) = (0.82 ± 0.05) × 10-12, k3( T) = (1.29 ± 0.19) × 10-11 exp(-(805 ± 43)/ T); and k4(294 K) = (1.12 ± 0.10) × 10-12, k4( T) = (1.80 ± 0.26) × 10-11 exp(-(816 ± 43)/ T). The cyclic molecules were found to be less reactive than the analogous linear molecule with the same number of -CH3 groups, while the linear and cyclic permethylsiloxane reactivity both increase with the increasing number of CH3- groups. The present results are compared with previous rate coefficient determinations where available. The permethylsiloxanes included in this study are atmospherically short-lived compounds with estimated atmospheric lifetimes of 11, 8, 17, and 13 days, respectively.

Reactivity of OH and CH3OH Between 22 and 64 K: Modelling the Gas Phase Production of CH3O in Barnard 1B.

In the last years, ultra-low temperature chemical kinetic experiments have demonstrated that some gas-phase reactions are much faster than previously thought. One example is the reaction between OH and CH3OH, which has been recently found to be accelerated at low temperatures yielding CH3O as main product. This finding opened the question of whether the CH3O observed in the dense core Barnard 1b could be formed by the gas-phase reaction of CH3OH and OH. Several chemical models including this reaction and grain-surface processes have been developed to explain the observed abundance of CH3O with little success. Here we report for the first time rate coefficients for the gas-phase reaction of OH and CH3OH down to a temperature of 22 K, very close to those in cold interstellar clouds. Two independent experimental set-ups based on the supersonic gas expansion technique coupled to the pulsed laser photolysis-laser induced fluorescence technique were used to determine rate coefficients in the temperature range 22-64 K. The temperature dependence obtained in this work can be expressed as k(22-64 K) = (3.6 ± 0.1) × 10-12(T/300 K)-(1.0±0.2) cm3 molecule-1 s-1. Implementing this expression in a chemical model of a cold dense cloud results in CH3O/CH3OH abundance ratios similar or slightly lower than the value of ∼ 3 × 10-3 observed in Barnard 1b. This finding confirms that the gas-phase reaction between OH and CH3OH is an important contributor to the formation of interstellar CH3O. The role of grain-surface processes in the formation of CH3O, although it cannot be fully neglected, remains controversial.

Assessment of the atmospheric loss processes initiated by OH radicals and sunlight, and the radiative efficiency for a series of hydrofluoroolefins, CF3(CF2)x=1,3,5CH[dbnd]CH2

Hydrofluoroolefins (HFOs) of the type CF3(CF2)x≥0CHCH2, are currently being suggested as substitutes of some hydrofluorocarbons (HFCs). In this work, an assessment of the atmospheric removal of CF3(CF2)x=1,3,5CHCH2, initiated by reaction with hydroxyl (OH) radicals and UV solar radiation is addressed. For that purpose, the rate coefficients for the OH + CF3(CF2)x=1,3,5CHCH2 reaction, kOH(T = 263–358 K), were determined by the pulsed laser photolysis-laser induced fluorescence technique. A slightly negative temperature dependence of kOH was observed, obtaining Ea/R (in K) values of −124 ± 15, −128 ± 6 and −160 ± 10, for CF3CF2CHCH2, CF3(CF2)3CHCH2 and CF3(CF2)5CHCH2, respectively. The estimated atmospheric lifetimes are around 8 days, considering that HFOs are well-mixed in the troposphere. Furthermore, an evaluation of the long-wave and short-wave absorption process of these HFOs have been carried out by determining the UV (191–367 nm) and IR (4000-500 cm−1) absorption cross sections at 298 K. Based on the obtained UV absorption cross sections, no photolysis of CF3(CF2)x=1,3,5CHCH2 is expected in the troposphere (λ > 290 nm). These species strongly absorb IR radiation in the atmospheric IR window. Despite the strong absorption in the IR region, the lifetime corrected radiative efficiencies are low (0.033 W m−2 ppb−1 for CF3(CF2)3CHCH2 and 0.039 Wm−2 ppb−1 for CF3(CF2)5CHCH2). Calculation of GWPs for these species has been performed as a function of the horizon time, providing values higher than unity for a short-period term, decreasing dramatically for longer periods. Therefore, it is concluded that emissions of these species do not affect the radiative forcing of climate, making them suitable replacements of large-GWP HFCs.

Low temperature rate coefficients for reactions of the butadiynyl radical, C4H, with various hydrocarbons. Part II: reactions with alkenes (ethylene, propene, 1-butene), dienes (allene, 1,3-butadiene) and alkynes (acetylene, propyne and 1-butyne)

The kinetics of the reactions of the linear butadiynyl radical, C4H (CCCCH), with a variety of unsaturated hydrocarbons have been studied over the temperature range of 39-300 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme, or reaction kinetics in uniform supersonic flow) apparatus combined with the pulsed laser photolysis-laser induced fluorescence technique. The rate coefficients for all the reactions studied are found to all be in excess of 10(-10) cm(3) molecule(-1) s(-1) over the entire temperature range. They can be fitted with the following expressions (valid from 39 K to 300 K, with RMS deviations of the experimental points from the predicted values shown, to which should be added 10% possible systematic error) for reaction of C4H with alkenes: k(C2H4) = (1.95 +/- 0.17) x 10(-10) (T/298 K)(-0.40) exp(9.4 K/T) cm3 molecule(-1) s(-1); k(C3H6) = (3.25 +/- 0.12) x 10(-10) (T/298 K)(-0.84) exp(-48.9 K/T) cm3 molecule(-1) s(-1); k(1-C4H8) = (6.30 +/- 0.35) x 10(-10) (T/298 K)(-0.61) exp(-65.0 K/T) cm3 molecule(-1) s(-1), for reaction of C4H with dienes: k(C3H4) = (3.70 +/- 0.34) x 10(-10) (T/298 K)(-1.18) exp(-91.1 K/T) cm3 molecule(-1) s(-1); k(1,3-C4H6) = (5.37 +/- 0.30) x 10(-10) (T/298 K)(-1.25) exp(-116.8 K/T) cm3 molecule(-1) s(-1), and for reaction of C4H with alkynes: k(C2H2) = (1.82 +/- 0.19) x 10(-10) (T/298 K)(-1.06) exp(-65.9 K/T) cm3 molecule(-1) s(-1); k(C3H4) = (3.20 +/- 0.08) x 10(-10) (T/298 K)(-0.82) exp(-47.5 K/T) cm3 molecule(-1) s(-1); k(1-C4H6) = (3.48 +/- 0.14) x 10(-10) (T/298 K)(-0.65) exp(-58.4 K/T) cm3 molecule(-1) s(-1). Possible reaction mechanisms and product channels are discussed in detail for each of these reactions. Potential implications of these results for models of low temperature chemical environments, in particular cold interstellar clouds and star-forming regions, are considered.

Low temperature rate coefficients for reactions of the butadiynyl radical, C4H, with various hydrocarbons. Part I: reactions with alkanes (CH4, C2H6, C3H8, C4H10)

The kinetics of the reactions of the linear butadiynyl radical, C4H (CCCCH), with methane, ethane, propane and butane have been studied over the temperature range of 39-300 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Uniform Supersonic Flow) apparatus combined with the pulsed laser photolysis-laser induced fluorescence technique. The rate coefficients, except for the reaction with methane, show a negative temperature dependence and can be fitted with the following expressions over the temperature range of this study: k(C2H6) = 0.289 x 10(-10) (T/298 K)(-1.23) exp(-24.8 K/T) cm3 molecule(-1) s(-1); k(C3H8) = 1.06 x 10(-10) (T/298 K)(-1.36) exp(-56.9 K/T) cm3 molecule(-1) s(-1); k(C4H10) = 2.93 x 10(-10) (T/298 K)(-1.30) exp(-90.1 K/T) cm3 molecule(-1) s(-1). The rate coefficients for the reaction with methane were measured only at 200 K and 300 K yielding a positive temperature dependence: k(CH4) = 1.63 x 10(-11) exp(-610 K/T) cm3 molecule(-1) s(-1). Possible reaction mechanisms and product channels are discussed in detail for each of these reactions. Potential implications of these results for models of low temperature chemical environments, in particular cold interstellar clouds and planetary atmospheres such as that of Titan, are considered.

Experimental measurements of low temperature rate coefficients for neutral–neutral reactions of interest for atmospheric chemistry of Titan, Pluto and Triton: Reactions of the CN radical

The kinetics of the reactions of cyano radical, CN (X2sigma+) with three hydrocarbons, propane (CH3CH2CH3), propene (CH3CH=CH2) and 1-butyne (CH[triple band]CCH2CH3) have been studied over the temperature range of 23-298 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Uniform Supersonic Flow) apparatus combined with the pulsed laser photolysis-laser induced fluorescence technique. These reactions are of interest for the cold atmospheres of Titan, Pluto and Triton, as they might participate in the formation of nitrogen and carbon bearing molecules, including nitriles, that are thought to play an important role in the formation of hazes and biological molecules. All three reactions are rapid with rate coefficients in excess of 10(-10) cm3 molecule(-1) s(-1) at the lowest temperatures of this study and show behaviour characteristic of barrierless reactions. Temperature dependences, different for each reaction, are compared to those used in the most recent photochemical models of Titan's atmosphere.

Reaction Rate Coefficients of OH Radicals and Cl Atoms with Ethyl Propanoate,n-Propyl Propanoate, Methyl 2-Methylpropanoate, and Ethyln-Butanoate

Kinetics of the reactions of OH radicals and Cl atoms with four saturated esters have been investigated. Rate coefficients for the gas-phase reactions of OH radicals with ethyl propanoate (k(1)), n-propyl propanoate (k(2)), methyl 2-methylpropanoate (k(3)), and ethyl n-butanoate (k(4)) were measured using a conventional relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. At (296 +/- 2) K, the rate coefficients obtained by the two methods were in good agreement. Significant curvatures in the Arrhenius plots have been observed in the temperature range 243-372 K for k(1), k(3), and k(4). The rate coefficients for the reactions of the four esters with Cl atoms were determined using the relative rate method at (296 +/- 2) K and atmospheric pressure. The values obtained are presented, compared with the literature values when they exist, and discussed. Reactivity trends and atmospheric implications for these esters are also presented.

Photodissociation of 3-Bromo-1,1,1-trifluoro-2-propanol at 193 nm: Laser-Induced Fluorescence Detection of OH(ν′′ = 0, J′′)

Photodissociation of 3-bromo-1,1,1-trifluoro-2-propanol (BTFP) has been investigated at 193 nm, employing the laser photolysis laser-induced fluorescence technique. The nascent OH product was detected state selectively, and the energy released into translation, rotation, and vibration of the photoproducts has been measured. OH is produced mostly vibrationally cold, with a moderate rotational excitation, which is characterized by a rotational temperature of 640 +/- 140 K. However, an appreciable amount of the available energy of 36.1 kcal mol(-1) is released into translation of OH (15.1 kcal mol(-1)). OH product has no preference for a specific spin-orbit state, Pi(3/2) or Pi(1/2). However, between two Lambda-doublet states, Pi(+) and Pi(-), the OH product has a preference for the former by a factor of 2. A mechanism of OH formation from BTFP on excitation at 193 nm is proposed, which involves first the direct C-Br bond dissociation from a repulsive state (n(Br)sigma*(C-Br)) as a primary process. The primary product, F(3)C-CH(OH)-CH(2), with sufficient internal energy undergoes spontaneous C-OH bond dissociation, through a loose transition state. The formation rate of OH is calculated to be 5.8 x 10(6) s(-1) using Rice-Ramsperger-Kassel-Marcus unimolecular rate theory. Experimental results have been supported by theoretical calculations, and energies of various low-energy dissociation channels of the primary product, F(3)C-CH(OH)-CH(2), have been calculated.

Rate Coefficients for the Reactions of C2(a3Πu) and C2(X1Σg+) with Various Hydrocarbons (CH4, C2H2, C2H4, C2H6, and C3H8): A Gas-Phase Experimental Study over the Temperature Range 24−300 K

The kinetics of reactions of C2(a(3)Pi(u)) and C2(X(1)Sigma(g)(+)) with various hydrocarbons (CH4, C2H2, C2H4, C2H6, and C3H8) have been studied in a uniform supersonic flow expansion over the temperature range 24-300 K. Rate coefficients have been obtained by using the pulsed laser photolysis-laser induced fluorescence technique, where both radicals were produced at the same time but detected separately. The reactivity of the triplet state was found to be significantly lower than that of the singlet ground state for all reactants over the whole temperature range of the study. Whereas C2(X(1)Sigma(g)(+)) reacts with a rate coefficient close to the gas kinetic limit with all hydrocarbons studied apart from CH4, C2(a(3)Pi(u)) appears to be more sensitive to the molecular and electronic structure of the reactant partners. The latter reacts at least one order of magnitude faster with unsaturated hydrocarbons than with alkanes, and the rate coefficients increase very significantly with the size of the alkane. Results are briefly discussed in terms of their potential astrophysical impact.

Rate Coefficients for the Reaction of OH with a Series of Unsaturated Alcohols between 263 and 371 K

Rate coefficients for the gas-phase reactions of OH radicals with four unsaturated alcohols, 3-methyl-3-buten-1-ol (k1), 2-buten-1-ol (k2), 2-methyl-2-propen-1-ol (k3) and 3-buten-1-ol (k4), were measured using two different techniques, a conventional relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. The Arrhenius rate coefficients (in units of cm(3) molecule(-1) s(-1)) over the temperature range 263-371 K were determined from the kinetic data obtained as k1 = (5.5 +/- 1.0) x 10(-12) exp [(836 +/- 54)/T]; k2 = (6.9 +/- 0.9) x 10(-12) exp [(744 +/- 40)/T]; k3 = (10 +/- 1) x 10(-12) exp [(652 +/- 27)/T]; and k4 = (4.0 +/- 0.4) x 10(-12) exp [(783 +/- 32)/T]. At 298 K, the rate coefficients obtained by the two methods for each of the alcohols studied were in good agreement. The results are presented and compared with those obtained previously for the same and related reactions of OH radicals. Reactivity factors for substituent groups containing the hydroxyl group are determined. The atmospheric implications for the studied alcohols are considered briefly.

OH reaction rate constants and UV absorption cross-sections of unsaturated esters

Absolute rate coefficients have been determined for the gas-phase reactions of hydroxyl radicals with methyl acrylate ( k 1), methyl methacrylate ( k 2) and ethyl acrylate ( k 3). Experiments were performed using two different techniques, the relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. The kinetic data obtained were used to derive the following Arrhenius expressions in the temperature range 253–374 K (in units of cm 3 molecule −1 s −1): k 1 = ( 2.0 ± 0.8 ) × 1 0 - 12 exp [ ( 553 ± 51 ) / T ] , k 2 = ( 2.5 ± 0.8 ) × 1 0 - 12 exp [ ( 821 ± 55 ) / T ] , k 3 = ( 2.3 ± 0.8 ) × 1 0 - 12 exp [ ( 580 ± 65 ) / T ] . At 298 K, the reaction rate constants obtained by the two methods were in good agreement. In addition, the UV absorption spectra for the three unsaturated esters have been determined at (298±2) K and the absorption cross-sections in the wavelength region 215–298 nm were reported. The results are presented, discussed and used to estimate the atmospheric lifetimes for the studied esters.

A Kinetic and Mechanistic Study of the Reactions of OH Radicals and Cl Atoms with 3,3,3-Trifluoropropanol under Atmospheric Conditions

Product distribution studies of the OH radical and Cl atom initiated oxidation of CF3CH2CH2OH in air at 1 atm and 298 +/- 5 K have been carried out in laboratory and outdoor atmospheric simulation chambers in the presence and absence of NOx. The results show that CF3CH2CHO is the only primary product and that the aldehyde is fairly rapidly removed from the system. In the absence of NOx the major degradation product of CF3CH2CHO is CF3CHO, and the combined yields of the two aldehydes formed from CF3CH2CH2OH are close to unity (0.95 +/- 0.05). In the presence of NOx small amounts of CF3CH2C(O)O2NO2 were also observed (<15%). At longer reaction times CF3CHO is removed from the system to give mainly CF2O. The laser photolysis-laser induced fluorescence technique was used to determine values of k(OH + CF3CH2CH2OH) = (0.89 +/- 0.03) x 10(-12) and k(OH + CF3CH2CHO) = (2.96 +/- 0.04) x 10(-12) cm3 molecule(-1) s(-1). A relative rate method has been employed to measure the rate coefficients k(OH + CF3CH2CH2OH) = (1.08 +/- 0.05) x 10(-12), k(OH + C6F13CH2CH2OH) = (0.79 +/- 0.08) x 10(-12), k(Cl + CF3CH2CH2OH) = (22.4 +/- 0.4) x 10(-12), and k(Cl + CF3CH2CHO) = (25.7 +/- 0.4) x 10(-12) cm3 molecule(-1) s(-1). The results from this investigation are discussed in terms of the possible importance of emissions of fluorinated alcohols as a source of fluorinated carboxylic acids in the environment.

Kinetics of the reactions of the OH radical with 2-methyl-1-propanol, 3-methyl-1-butanol and 3-methyl-2-butanol between 241 and 373 K

Absolute rate constants have been measured for the gas-phase reactions of hydroxyl radicals with 2-methyl-1-propanol (k1), 3-methyl-1-butanol (k2) and 3-methyl-2-butanol (k3). Experiments were carried out using two different techniques, the relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. The kinetic data were used to derive the following Arrhenius expressions in the temperature range 241–373 K(in units of cm3 molecule−1 s−1):k1 = (3.1±0.9) × 10−12exp[(352±82)/T]k2 = (2.8±0.9) × 10−12exp[(503±98)/T]k3 = (2.6±0.6) × 10−12exp[(456±65)/T]At 298 K, the reaction rate constants obtained by the two methods were in very good agreement. The results are presented, discussed and used to estimate the atmospheric lifetimes for the studied alcohols.

Temperature dependence of the limiting low- and high-pressure rate constants for the CH 3O+NO 2+He reaction over the 250–390 K temperature range

The laser photolysis laser-induced fluorescence technique was used to measure the pressure ( p T=50–600 Torr) and temperature ( T=250–390 K) dependence of the rate constant for the CH 3O+NO 2 reaction in He. CH 3ONO/NO 2/He mixtures were photolysed at 248 nm and the CH 3O radical generated was monitored by LIF emission. Combined with previously reported rate coefficients at low pressures and after subtracting the disproportionation contribution to this reaction, our corrected kinetic experimental data, k 1a( T), were fitted to the Troe expression, yielding the limiting low- ( k 1a 0) and high-pressure ( k 1a ∞) rate constants. The temperature dependence found was (k 1 a 0±2σ)=(3.93±0.05)×10 −29(T/300) −(1.74±0.40) cm 6 molecule −2 s −1 and (k 1 a ∞±2σ)=(2.40±0.02)×10 −11(T/300) −(0.88±0.32) cm 3 molecule −1 s −1 . These results are compared with those previously reported at room temperature.

Kinetic Studies of OH Reactions with a Series of Ketones

Absolute rate constants have been measured for the gas phase reactions of hydroxyl radicals with a series of aliphatic acetates: methyl acetate (k1), ethyl acetate (k2), n-propyl acetate (k3), n-butyl acetate (k4), and n-pentyl acetate (k5). Experiments were carried out using the pulsed laser photolysislaser induced fluorescence technique over the temperature range 243−372 K. The obtained kinetic data were used to derive the Arrhenius expressions, and since the Arrhenius plots were slightly curved they were fitted, using a three-parameter expression. The Arrhenius expressions obtained are: k1 = (0.53 ± 0.09) × 10-12 exp[−(128 ± 102)/T] ; k2 = (0.48 ± 0.09) × 10-12 exp[(397 ± 103)/T]; k3 = (1.03 ± 0.12) × 10-12 exp[(370 ± 69)/T] ; k4 = (2.10 ± 0.28) × 10-12 exp[(299 ± 81)/T], and k5 = (2.75 ± 0.46) × 10-12 exp[(302 ± 102)/T] (in units of cm3 molecule-1 s-1). At room temperature, the rate constants obtained (in units of 10-12 cm3 molecule-1 s-1) were as follows: methyl acetate, 0.32 ± 0.03; ethyl acetate...