Bath Gas Research Articles

Time-resolved gas-phase kinetic study of the germylene addition reaction, GeH2 + CH3CCCH3

Time-resolved kinetic studies of the reaction of germylene, GeH2, generated by laser flash photolysis of 3,4-dimethyl-1-germacyclopent-3-ene, have been carried out to obtain rate constants for its bimolecular reaction with 2-butyne, CH3C[triple bond, length as m-dash]CCH3. The reaction was studied in the gas phase over the pressure range 1-100 Torr in SF6 bath gas, at five temperatures in the range 300-556 K. The second order rate constants obtained by extrapolation to the high pressure limits at each temperature, fitted the Arrhenius equation: log(kinfinity/cm3 molecule(-1) s(-1)=(-10.46+/-0.06)+(5.16+/-0.47) kJ mol(-1)/RT ln 10. Calculations of the energy surface of the GeC4H8 reaction system were carried out employing the additivity principle, by combining previous quantum chemical calculations of related reaction systems. These support formation of 1,2-dimethylvinylgermylene (rather than 2,3-dimethylgermirene) as the end product. RRKM calculations of the pressure dependence of the reaction are in reasonable agreement with this finding. The reactions of GeH2 with C2H2 and with CH3C[triple bond, length as m-dash]CCH3 are compared and contrasted.

Photolysis of CH3C(O)CH3 at 248 and 266 nm: pressure and temperature dependent overall quantum yields

The overall quantum yield of photolysis of acetone (CH(3)C(O)CH(3)) at 248 and 266 nm was measured using the pulsed laser photolysis technique. The organic photo-fragment radicals CH(3) and CH(3)CO were detected indirectly as Br atoms using time-resolved resonance fluorescence following their reaction with Br(2). Quantum yields for acetone photolysis were derived relative to COCl(2) (at 248 nm) or Cl(2) (at 266 nm) in back-to-back experiments in which Cl atoms were scavenged by Br(2) to form Br. At 248 nm, experiments were carried out at pressures between 60 and 760 Torr of N(2) and at three temperatures: 224, 234 and 298 K. At this wavelength, the overall quantum yield was 0.98 +/- 0.10 and, within experimental uncertainty, was independent of pressure and temperature in the ranges covered. At 266 nm, experiments were restricted to 298 K, where the quantum yield was also close to unity, but with a weak dependence on bath gas pressure. These results confirm our previous room temperature, 266 nm dataset obtained using a different experimental approach in which the yield of CH(3) was measured directly.

Determination of the Rate Constant for the NH2(X2B1) + NH2(X2B1) Reaction at Low Pressure and 293 K

The rate constant for the reaction NH(2)(X(2)B(1)) + NH(2)(X(2)B(1)) --> products was measured in CF(4), N(2) and Ar carrier gases at 293 +/- 2 K over a pressure range from 2 to 10 Torr. The NH(2) radical was produced by the 193 nm photolysis of NH(3) dilute in the carrier gas. Both the loss of NH(3) and its subsequent recovery and the production of NH(2) and subsequent reaction were monitored simultaneously following the photolysis laser pulse. Both species were detected using quantitative time-resolved high-resolution absorption spectroscopy. The NH(3) molecule was monitored in the NIR using a rotation transition of the nu(1) + nu(3) first combination band near 1500 nm, and the NH(2) radical was monitored using the (1)2(21) <-- (1)3(31) rotational transition of the (0,7,0)A(2)A(1) <-- (0,0,0) X(2)B(1) band near 675 nm. The low-pressure rate constant showed a linear dependence on pressure. The slope of the pressure dependence was dominated by a recombination rate constant for NH(2) + NH(2) given by (8.0 +/- 0.5) x 10(-29), (5.7 +/- 0.7) x 10(-29), and (3.9 +/- 0.4) x 10(-29) cm(6) molecule(-2) s(-1) in CF(4), N(2), and Ar bath gases, respectively, where the uncertainties are +/-2sigma in the scatter of the measurements. The average of the three independent measurements of the sum of the disproportionation rate constants (the zero pressure rate constant) was (3.4 +/- 6) x 10(-13) cm(3) molecule(-1) s(-1), where the uncertainty is +/-2sigma in the scatter of the measurements.

Pressure Broadening of H2O Absorption Lines in the 1.3 μm Region Measured by Continuous Wave-Cavity Ring-Down Spectroscopy: Application in the Trace Detection of Water Vapor in N2, SiH4, CF4, and PH3

A continuous wave cavity ring-down (cw-CRD) spectrometer has been developed for the measurement of trace levels of water vapor by absorption spectroscopy at wavelengths in the vicinity of 1358 nm and 1392 nm. The speed of data acquisition and selectivity make cavity ringdown spectroscopy potentially more useful than current techniques for measurement of trace water in process gases and vacuum environments used for semiconductor manufacture where water vapor contamination has a detrimental effect on the final product. The pressure broadening coefficients (gamma) for bath gases N(2), air, and Ar and semiconductor process gases SiH(4), PH(3), and CF(4) were determined for a range of absorption lines in the 2nu(1) and nu(1) + nu(3) bands of H(2)O. For the transitions investigated, the concentration of water vapor in the sample gas varied from 1.7 x 10(12) to 2.9 x 10(15) molecule cm(-3) in N(2) at a total pressure of <10 mbar and was mixed with the bath gas of increasing pressure up to approximately 200 mbar. The values of gamma quantify the reduction in peak absorption cross-sections with bath gas pressure and, thus, their effects on the detection limit of water vapor. For a CRD spectrometer with a ring-down time of tau = 12.0 mus measured with a precision of 0.6%, detection limits for the measurement of water vapor in 1 atm N(2) and of CF(4) were estimated to be 18 and 14 ppbv, respectively. Competing absorption by SiH(4) and PH(3) in the 1.3 mum wavelength region results in respective detection limits for water vapor of 98 and 319 ppbv (relative to 1 atm) in 0.2 atm SiH(4) and 0.37 atm PH(3).

Reaction Bonded Silicon Nitride - Silicon Carbide and SiAlON - Silicon Carbide Refractories for Aluminium Smelting

The widely used Si3N4-SiC sidewall refractories for aluminum smelting cells, and β SiAlON-SiC composites that can be potentially used for this purpose, have been produced by reaction bonding and their corrosion performance assessed in simulated aluminum electrochemical cell conditions. The formation of the Si3N4 and SiAlON phases were studied by reaction bonding of silicon powders in a nitrogen atmosphere at low temperatures to promote the formation of silicon nitride, followed by a higher heating step to produce β SiAlON composites of different composition. The corrosion performance was studied in a laboratory scale aluminum electrolysis cell where samples were exposed to both liquid attack from molten salt bath and corrosive gas attack. The corrosion resistance of the samples was shown to be dependent on the composition but more importantly on the environment during corrosion, with samples in the gas phase showing higher corrosion.

Ultraviolet Photolysis of HCHO: Absolute HCO Quantum Yields by Direct Detection of the HCO Radical Photoproduct

Absolute quantum yields for the radical (H + HCO) channel of HCHO photolysis, Phi(HCO), have been measured for the tropospherically relevant range of wavelengths (lambda) between 300 and 330 nm. The HCO photoproduct was directly detected by using a custom-built, combined ultra-violet (UV) absorption and cavity ring down (CRD) detection spectrometer. This instrument was previously employed for high-resolution (spectral resolution approximately 0.0035 nm) measurements of absorption cross-sections of HCHO, sigma(HCHO)(lambda), and relative HCO quantum yields. Absolute Phi(HCO) values were measured at seven wavelengths, lambda = 303.70, 305.13, 308.87, 314.31, 320.67, 325.59, and 329.51 nm, using an independent calibration technique based on the simultaneous UV photolysis of HCHO and Cl(2). These Phi(HCO) measurements display greater variability as a function of wavelength than the current NASA-JPL recommendations for Phi(HCO). The absolute Phi(HCO)(lambda) determinations and previously measured sigma(HCHO)(lambda) were used to scale an extensive set of relative HCO yield measurements. The outcome of this procedure is a full suite of data for the product of the absolute radical quantum yield and HCHO absorption cross-section, Phi(HCO)(lambda)sigma(HCHO)(lambda), at wavelengths from 302.6 to 331.0 nm with a wavelength resolution of 0.005 nm. This product of photochemical parameters is combined with high-resolution solar photon flux data to calculate the integrated photolysis rate of HCHO to the radical (H + HCO) channel, J(HCO). Comparison with the latest NASA-JPL recommendations, reported at 1 nm wavelength resolution, suggests an increased J(HCO) of 25% at 0 degrees solar zenith angle (SZA) increasing to 33% at high SZA (80 degrees). The differences in the calculated photolysis rate compared with the current HCHO data arise, in part, from the higher wavelength resolution of the current data set and highlight the importance of using high-resolution spectroscopic techniques to achieve a complete and accurate picture of HCHO photodissociation processes. All experimental Phi(HCO)(lambda)sigma(HCHO)(lambda) data are available for the wavelength range 302.6-331.0 nm (at 294 and 245 K and under 200 Torr of N(2) bath gas) as Supporting Information with wavelength resolutions of 0.005, 0.1, and 1.0 nm. Equivalent data sets of Phi(H(2)+CO)(lambda)sigma(HCHO)(lambda) for the molecular (H(2) + CO) photofragmentation channel, produced using the measured Phi(HCO)(lambda) sigma(HCHO)(tau) values, are also provided at 0.1 and 1.0 nm resolution.

Experimental and Theoretical Study of the Carbon-13 and Deuterium Kinetic Isotope Effects in the Cl and OH Reactions of CH3F

A laser flash photolysis-resonance fluorescence technique has been employed to determine absolute rate coefficients for the CH3F + Cl reaction in N2 bath gas in the temperature range of 200-700 K and pressure range of 33-133 hPa. The data were fitted to a modified Arrhenius expression k(T) = 1.14 x 10(-12) x (T/298)2.26 exp{-313/T}. The OH and Cl reaction rates of (13)CH3F and CD3F have been measured by long-path FTIR spectroscopy relative to CH3F at 298 +/- 2 K and 1013 +/- 10 hPa in purified air. The FTIR spectra were fitted using a nonlinear least-squares spectral fitting method including line data from the HITRAN database and measured infrared spectra as references. The relative reaction rates defined by alpha = k(light)/k(heavy) were determined to be k(OH+CH3F)/k(OH+CD3F) = 4.067 +/- 0.018, k(OH+CH3F)/k(OH+(13)CH3F) = 1.067 +/- 0.006, k(Cl+CH3F)/k(Cl+CD3F) = 5.11 +/- 0.07, and k(Cl+CH3F)/k(Cl+(13)CH3F) = 1.016 +/- 0.006. The carbon-13 and deuterium kinetic isotope effects in the OH and Cl reactions of CH3F have been further investigated by quantum chemistry methods and variational transition state theory.

OH time-histories during oxidation of n-heptane and methylcyclohexane at high pressures and temperatures

OH concentration time-histories during n-heptane and methylcyclohexane (MCH) oxidation were measured behind reflected shock waves in a heated, high-pressure shock tube. Experimental conditions covered temperatures of 1121 to 1332 K, pressures near 15 atm, and initial fuel concentrations of 750 and 1000 ppm (by volume), and an equivalence ratio of 0.5 with O 2 as the oxidizer and argon as the bath gas. OH concentrations were measured using narrow-linewidth ring-dye laser absorption near the R-branchhead of the OH A – X ( 0 , 0 ) system at 306.47 nm. These current measurements together with our recent results for n-dodecane oxidation [S.S. Vasu, D.F. Davidson, Z. Hong, V. Vasudevan, R.K. Hanson, Proc. Combust. Inst. 32 (2009), doi:10.1016/j.proci.2008.05.006] provide critically needed validation targets for jet fuel surrogate kinetic mechanisms and further improve understanding of high-pressure, high-temperature oxidation chemistry. Detailed comparisons of these OH time-histories with the predictions of various kinetic mechanisms were made. Sensitivity and pathway analyses for these reference fuel components were performed, leading to reaction rate recommendations with improved model performance. Current results are the first quantitative measurements of OH time-histories during high-pressure oxidation of these fuels, and hence are a critical step toward development of accurate reaction models for jet fuel surrogates.

Kinetic studies of chlorobenzene reactions with hydrogen atoms and phenyl radicals and the thermochemistry of 1-chlorocyclohexadienyl radicals

Atomic H and Cl were monitored by time-resolved resonance spectroscopy in the vacuum ultraviolet, following 193nm laser flash photolysis of C6H5Cl and mixtures with NH3, over 300–1020K and with Ar bath gas pressures from 30 to 440mbar. Below 550K simple exponential decays of [H] were observed, and attributed to addition to form chlorocyclohexadienyl radicals. This addition was reversible over 550–630K and the equilibrium constant was determined by a third law approach. The addition rate constant can be summarized as (1.51±0.11)×10−11exp((−1397±29)/T) cm3molecule−1s−1 (300–630K, 1σ uncertainties), and the C–H bond dissociation enthalpy in 1-chlorocyclohexadienyl was determined to be 108.1±3.3kJmol−1 at 298K. At higher temperatures the photolysis of chlorobenzene yielded H atoms, which is attributed to the reaction of phenyl with chlorobenzene with a rate constant of (4.5±1.8)×10−10exp((−4694±355)/T) cm3 molecule−1s−1 over 810–1020K. These and other reaction pathways are discussed in terms of information about the potential energy surface obtained via B3LYP/6-311G(2d,d,p) density functional theory.

Development of a low power, high mass range mass spectrometer for Mars surface analysis

A compact, low power quadrupole ion trap mass spectrometer is being developed that will achieve a mass range of 2000 Da at low voltage (0–300 V 0–p) using a lower frequency fundamental voltage and supplemental excitation to very low q excitation parameter. The instrument is a prototype for a spacecraft hardware design referred to as the Mars Organic Mass Analyzer (MOMA) that is currently scheduled for flight to Mars in 2013 as part of the European Space Agency ExoMars mission. MOMA is one of two “life detection” instruments that are being sponsored by NASA. MOMA will accommodate both an atmospheric pressure laser desorption ionization source that will provide direct sampling of core samples for the detection of organics over a broad mass range and an electron ionization source coupled to a gas chromatograph for the detection of atmospheric gases and specific biomarkers (e.g., amino acids, nucleobases, etc.). The instrument reported herein is an early prototype used to demonstrate the basic design concepts for a low power instrument with high mass range, including the use of supplemental frequency scans to record mass spectra. In addition, mass spectra are obtained using CO 2 (the major constituent of the Mars atmosphere) as the bath gas, and a novel internal electron ionization source has been developed in which the electron beam enters through the ring electrode.

The Addition Reaction between Silylene and Ethyne: Further Isotope Studies, Pressure Dependence Studies, and Quantum Chemical Calculations

Time-resolved kinetic studies of the reaction of dideutero-silylene, SiD 2, generated by laser flash photolysis of phenylsilane-d 3, have been carried out to obtain rate constants for its bimolecular reaction with C 2H 2. The reaction was studied in the gas phase over the pressure range 1-100 Torr in SF 6 bath gas, at five temperatures in the range 297-600 K. The second-order rate constants obtained by extrapolation to the high-pressure limits at each temperature fitted the Arrhenius equation log( k (infinity)/cm (3) molecule (-1) s (-1)) = (-10.05 +/- 0.05) + (3.43 +/- 0.36 kJ mol (-1))/ RT ln 10. The rate constants were used to obtain a comprehensive set of isotope effects by comparison with earlier obtained rate constants for the reactions of SiH 2 with C 2H 2 and C 2D 2. Additionally, pressure-dependent rate constants for the reaction of SiH 2 with C 2H 2 in the presence of He (1-100 Torr) were obtained at 300, 399, and 613 K. Quantum chemical (ab initio) calculations of the SiC 2H 4 reaction system at the G3 level support the initial formation of silirene, which rapidly isomerizes to ethynylsilane as the major pathway. Reversible formation of vinylsilylene is also an important process. The calculations also indicate the involvement of several other intermediates, not previously suggested in the mechanism. RRKM calculations are in semiquantitative agreement with the pressure dependences and isotope effects suggested by the ab initio calculations, but residual discrepancies suggest the possible involvement of the minor reaction channel, SiH 2 + C 2H 2 --> Si( (3)P 1) + C 2H 4. The results are compared and contrasted with previous studies of this reaction system.

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].

The CH 3CO quantum yield in the 248 nm photolysis of acetone, methyl ethyl ketone, and biacetyl

We report measurements of the CH 3CO quantum yield, Φ C H 3 CO , following the 248 nm pulsed laser photolysis of acetone (CH 3C(O)CH 3), methyl ethyl ketone (CH 3C(O)CH 2CH 3), and biacetyl (CH 3C(O)C(O)CH 3). CH 3CO quantum yields at 248 nm were measured at 296 K, relative to CH 3CO reference systems. CH 3CO was detected using cavity ring-down spectroscopy at wavelengths between 490 and 660 nm. Measurements were performed between 60 and 670 Torr (He, N 2 bath gases) and the obtained CH 3CO quantum yields in the low-pressure limit, Φ C H 3 CO 0 , were 0.535 ± 0.09, 0.41 ± 0.08, and 0.76 ± 0.11, for acetone, methyl ethyl ketone, and biacetyl, respectively. The quoted uncertainties are 2 σ (95% confidence level) and include estimated systematic errors. An increase in Φ C H 3 CO with increasing bath gas pressure, which depended on the identity of the collision partner (He, N 2), was observed. The present results are compared with previous quantum yield determinations.

Kinetics of the CCl 2 + Br 2 and CCl 2 + NO 2 reactions in the temperature range 266−365 K and reactivity of the CCl 2 biradical

The kinetics of the CCl 2 + Br 2 and CCl 2 + NO 2 reactions have been studied at temperatures between 266 and 365 K using laser photolysis/photoionization mass spectrometry. Dichloromethylene biradicals were produced by the pulsed laser photolysis of CCl 4. The bimolecular rate coefficients of the CCl 2 + Br 2 reaction can be described by the Arrhenius expression k 1 = (7.05 ± 1.75) × 10 −12 exp[(3.52 ± 0.63) kJ mol −1/ RT] cm 3 molecule −1 s −1. CCl 2Br was observed as a primary product of this reaction. Interestingly, the bimolecular rate coefficients of the CCl 2 + NO 2 reaction were observed to depend weakly on the bath gas density and to possess a negative temperature dependence.

Shock-Tube Study of the Thermal Decomposition of CH3CHO and CH3CHO + H Reaction

The thermal decomposition of acetaldehyde, CH3CHO + M --> CH3 + HCO + M (eq 1), and the reaction CH3CHO + H --> products (eq 6) have been studied behind reflected shock waves with argon as the bath gas and using H-atom resonance absorption spectrometry as the detection technique. To suppress consecutive bimolecular reactions, the initial concentrations were kept low (approximately 10(13) cm(-3)). Reaction was investigated at temperatures ranging from 1250 to 1650 K at pressures between 1 and 5 bar. The rate coefficients were determined from the initial slope of the hydrogen profile via k1 = [CH3CHO]0(-1) x d[H]/dt, and the temperature dependences observed can be expressed by the following Arrhenius equations: k1(T, 1.4 bar) = 2.9 x 10(14) exp(-38 120 K/T) s(-1), k1(T, 2.9 bar) = 2.8 x 10(14) exp(-37 170 K/T) s(-1), and k1(T, 4.5 bar) = 1.1 x 10(14) exp(-35 150 K/T) s(-1). Reaction was studied with C2H5I as the H-atom precursor under pseudo-first-order conditions with respect to CH3CHO in the temperature range 1040-1240 K at a pressure of 1.4 bar. For the temperature dependence of the rate coefficient the following Arrhenius equation was obtained: k6(T) = 2.6 x 10(-10) exp(-3470 K/T) cm(3) s(-1). Combining our results with low-temperature data published by other authors, we recommend the following expression for the temperature range 300-2000 K: k6(T) = 6.6 x 10(-18) (T/K) (2.15) exp(-800 K/T) cm(3) s(-1). The uncertainties of the rate coefficients k1 and k6 were estimated to be +/-30%.

Kinetics of the radical reactions in pulse radiolyzed RHF — CO2(SF6)-O2-NO gaseous mixtures; RHF = CH3CH2F, CH3CHF2, CH3CF3, CH2FCF3

the literature values. The bath gases (SF6 or CO2) have got minor effect on the rate constants of RHFO2+NO→NO2+prod. reactions; RHFO2 = CH3CH2O2, CH3CHFO2, CH3CF2O2, CF3CH2O2, CF3CHFO2. The obtained rate coefficients are in the scope of the literature values, although they are lower than those recommended in NIST database. The reasons are discussed.

Gas‐phase reactions of Cl atoms with hydrochloroethers: relative rate constants and their correlation with substituents' electronegativities

AbstractRate constants for the reactions of Cl atoms with CH3OCHCl2 and CH3OCH2CH2Cl were determined at (296 ± 2) K and atmospheric pressure using synthetic air as bath gas. Decay rates of these organic compounds were measured relative to the following reference compounds: CH2ClCH2Cl and n‐C5H12. Using rate constants of 1.33 × 10−12 and 2.52 × 10−10 cm3 molecule−1 sec−1 for the reaction of Cl atoms with CH2ClCH2Cl and n‐C5H12, respectively, the following rate coefficients were derived: k(Cl + CH3OCHCl2) = (1.05 ± 0.11) × 10−12 and k(Cl + CH3OCH2CH2Cl) = (1.14 ± 0.10) × 10−10, in units of cm3 molecule−1 s−1. The rate constants obtained were compared with previous literature data and a correlation was found between the rate coefficients of some CH3OCHR1R2 + Cl reactions and ΔElectronegativity of CHR1R2. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Yet another look at the reaction CH3 + H + M = CH4 + M

AbstractRate and equilibrium constant parameters for the title system have been evaluated. In general the format used by Baulch et al. (J Phys Chem Ref Data 2005, 34, 757) is compatible with the results. For Ar as the bath gas, the following parameters are suggested: k0 (cm6 molec−2 s−1) = 1.53 × 10−23 T−2.17 with Fc = 0.876 exp(−T/1801) + 0.124 exp(−T/33.1). k∞ = 3.5 × 10−10 cm3 molec−1 s−1 as suggested in Baulch et al. (2005). However, since master equation calculations based on a hindered‐Gorin transition state along with an exponential‐down energy transfer model (Golden et al., J Phys Chem 2003, 107, 11057–11057) have been carried out herein and compared with data, the results can be stored in lookup tables, avoiding errors introduced by universal expressions, or values can be computed on the fly using the parameters for the master equation calculation given in the paper. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 310–319, 2008

Approach to Thermal Equilibrium in Atomic Collisions

The energy relaxation of fast atoms moving in a thermal bath gas is explored experimentally and theoretically. Two time scales characterize the equilibration, one a short time, in which the isotropic energy distribution profile relaxes to a Maxwellian shape at some intermediate effective temperature, and the second, a longer time in which the relaxation preserves a Maxwellian distribution and its effective temperature decreases continuously to the bath gas temperature. The formation and preservation of a Maxwellian distribution does not depend on the projectile to bath gas atom mass ratio. This two-stage behavior arises due to the dominance of small angle scattering and small energy transfer in the collisions of neutral particles. Measurements of the evolving Doppler profiles of emission from excited initially energetic nitrogen atoms traversing bath gases of helium and argon confirm the theoretical predictions.

Kinetics of the reactions of Cl atoms with 2-buten-1-ol, 2-methyl-2-propen-1-ol, and 3-methyl-2-buten-1-ol as a function of temperature

The reactions of three structurally similar unsaturated alcohols, 2-buten-1-ol (crotyl alcohol), 2-methyl-2-propen-1-ol (MPO221) and 3-methyl-2-buten-1-ol (MBO321) with Cl atoms, have been investigated for the first time, using a 400 l Teflon reaction chamber coupled with gas chromatograph-coupled with flame-ionization detection (GC-FID). The experiments were performed at atmospheric pressure and at temperatures between 255 and 298 K, in air or nitrogen as the bath gas. The obtained kinetic data were used to derive the Arrhenius expressions \(k_{{\text{MPO221}}} = \left( {3.05 \pm 1.40} \right) \times 10^{ - 23} \exp {{\left( {8,760 \pm 1,279} \right)} \mathord{\left/ {\vphantom {{\left( {8,760 \pm 1,279} \right)} T}} \right. \kern-\nulldelimiterspace} T}\), \(k_{{\text{crotyl}}} = \left( {8.85 \pm 0.46} \right) \times 10^{ - 21} \exp {{\left( {7,240 \pm 1,455} \right)} \mathord{\left/ {\vphantom {{\left( {7,240 \pm 1,455} \right)} T}} \right. \kern-\nulldelimiterspace} T}\), \(k_{{\text{MBO321}}} = \left( {7.55 \pm 0.20} \right) \times 10^{ - 21} \exp {{\left( {7,361 \pm 735} \right)} \mathord{\left/ {\vphantom {{\left( {7,361 \pm 735} \right)} T}} \right. \kern-\nulldelimiterspace} T}\) (in units of cm3 molecule−1 s−1). Finally, atmospheric lifetimes of those unsaturated alcohols with respect to OH, NO3, O3 and Cl have been calculated.