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A Kinetic Study of the Reactions of OH with n-Undecane and n-Dodecane Using the RR/DF/MS Technique Michael Phan, and Zhuangjie Li J. Phys. Chem. A, Just Accepted Manuscript • Publication Date (Web): 03 May 2017 Downloaded from http://pubs.acs.org on May 8, 2017

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The Journal of Physical Chemistry

A Kinetics Study of the Reactions of OH with n-Undecane and n-Dodecane Using the RR/DF/MS Technique Michael Phan and Zhuangjie Li*

Department of Chemistry and Biochemistry, California State University-Fullerton, Fullerton, California 92834

Abstract The kinetics of the reactions of hydroxyl radical with n-undecane (n-C11H24) and n-dodecane (nC12H26) has been studied at 240 – 340 K and a total pressure of 1 Torr using the relative rate/discharge flow/ mass spectrometry (RR/DF/MS) technique. The rate constants at 298 K for these reactions were determined to be kn-undecane+OH = (1.59±0.24) x 10-11 cm3 molecule-1 s-1 and kn-dodecane+OH = (1.83 ± 0.26) x 10-11 cm3 molecule-1 s-1, respectively. The rate constants of these reactions were found to positively dependent on temperature at 277 – 340 K, and negatively dependent on temperature at 240 – 277 K. The atmospheric lifetime of these compounds are estimated to be 25.8 and 19.8 hours for n-undecane and n-dodecane respectively based the kinetics results in the present study.

*Corresponding author: Phone: (657)278-3585. Fax: (657)278-8010. E-mail: [email protected].

1 ACS Paragon Plus Environment


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Introduction n-undecane (n-C11H24) and n-dodecane (n-C12H26) are volatile organic compounds (VOCs) that are generated and emitted into the atmosphere from a number of anthropogenic activities, including petroleum and crude oil processing, organic synthesis, jet-fuel research, paraffin, rubber, and paper manufacturing, as well as industrial waste and automobile exhaust.1-3 As a results, significant amount of these compounds have been found in the atmosphere. nundecane has been detected at concentrations up to 4.89 ppb (parts per billion) in the atmosphere over airfields, roadways, populated urban, suburban areas, and lead and iron factories, and ndodecane has also been detected over urban and suburban areas across several countries with concentrations up to 23 ppb.3-10 The reaction of n-undecane and n-dodecane with hydroxyl radicals (OH), n-undecane + OH → products

(1)

n-dodecane + OH → products

(2)

plays an important role in the oxidative degradation processes of these compounds in the atmosphere. It is well known that the alkane degradation initiated by the OH radicals leads to formation of photochemical smog.11 Recent chamber studies also showed that the OH initiated n-undecane and n-dodecane degradation in the presence of NOx (i.e. NO + NO2) can result in production of secondary organic aerosols (SOAs).12-18 Thus it is imperative to acquire kinetics data for the reaction of n-undecane and n-dodecane with hydroxyl radicals in order to model the atmospheric composition in areas containing these air pollutants. There have been only two kinetics investigations for the reaction of hydroxyl radicals with n-undecane and n-dodecane.19,20 The first rate constant of reactions of n-undecane and ndodecane with OH radicals at 300 K was reported to be k1(300 K) = (1.33 ± 0.02) x 10-11 cm3 molecule-1 s-1 and k2(300 K) = (1.39 ± 0.01) x 10-11 cm3 molecule-1 s-1, respectively, by Behnke et al. using the relative rate technique with n-octane as a reference.19 Later Nolting et al. conducted a smog chamber study at 312 K using the relative rate technique with n-heptane as a reference, and they reported the rate constant for the reactions of n-undecane and n-dodecane with OH to be k1(312 K) = (1.36 ± 0.03) x 10-11 cm3 molecule-1 s-1 and k2(312 K) = (1.51 ± 0.05) x 10-11 cm3 molecule-1 s-1, respectively.20 To our best knowledge there were no temperature dependent kinetics measurements for reactions 1 and 2, especially at temperatures representative of troposphere. In this paper, we will report our kinetic study of reactions 1 and 2 at 240−340 K 2 ACS Paragon Plus Environment

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using the relative rate/discharge flow/mass spectrometry (RR/DF/MS) technique in order to enhance current kinetics database for atmospheric composition modeling.

Interesting

temperature dependent behavior of rate constant for the n-undecane and n-dodecane reactions with OH was observed at temperatures below 277 K, and a hypothesis for the possible reaction mechanisms leading to such observation is presented. Finally, the atmospheric lifetime for nundecane and n-dodecane is then estimated using our kinetics results determined at 277 K.

Experimental Section

The RR/DF/MS technique for kinetics investigation of the reactions of VOCs with OH radicals was developed in our laboratory, and the technique has been used to determine the rate constant of OH reaction with n-C6 - n-C10 alkanes as a function of temperature.21-23 Figure 1 shows the schematic of the RR/DF/MS apparatus used to study the kinetics of reactions 1 and 2. Briefly the flow reactor was made of a 100 cm Pyrex tube with an internal diameter of 5.08 cm. A Teflon sheet (0.79 mm thickness) was placed inside the reactor to reduce OH wall loss and prevent the reactor surface from being contaminated by the reaction products. The reactor was surrounded with a cooling jacket to regulate the reactor temperature in a range of 240 – 340 K for temperature dependent study of the rate constant of reactions 1 and 2. Methanol and water were used as temperature controlling fluids, and they were circulated through the jacket by a bath circulator (Neslab ULT-80) to achieve a temperature of 240 – 277 K and 298 – 340 K, respectively. Helium was used as a carrier gas, and a total flow of about 2,000 sccm (standard cube centimeter) of helium was employed to deliver the reactants into the flow reactor, which allowed an approximate contact time between OH and the alkanes to be about 20 ms. During the experiments the flow reactor was pumped by a mechanical pump (Edwards E2M175), and the pressure of the flow reactor was maintained at about 1 Torr by adjusting a throttle value downstream of the pipeline. A double sliding injector made of two concentric Pyrex tubes, with an interior diameters of 7 mm and 12.7 mm, was used for production of the OH radicals by allowing reaction of H2O molecules (carried by 100 sccm of He) with atomic fluorine (carried by 1500 sccm of He) that was generated by microwave discharge of 5% F2 in helium, F2 + microwave discharge → 2 F

(3)

F + H2O → OH + HF

(4)

k4= 1.4 x 10-11 cm3 molecule-1 s-1 24 3 ACS Paragon Plus Environment


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The interior of the 7 mm Pyrex tube was coated a layer of halocarbon wax (Halocarbon Products Corporation, series 1500) to avoid the contact between atomic fluorine and the SiO2 surface. The flow rate of the carrier gas delivering reactants and OH precursors was each regulated using a flow controller (Hastings Model 400). A liquid nitrogen trap was positioned downstream of the flow reactor to protect the mechanical pump from exposure to corrosive chemicals generated in the flow reactor. The target n-alkane and reference compounds samples were separately placed in two bubblers, and their vapor molecules were introduced into the flow reactor each by 200 sccm of helium. The reference (n-nonane or n-decane) vapor molecules were diffusing out of the sample bubbler, while the n-undecane and n-dodecane vapor molecules were pushed out of their sample bubblers by the carrier gas because of their low vapor pressure (0.44 Torr and 0.14 Torr at 25 °C for n-undecane and n-dodecane, respectively). To obtain large mass spectral signals for the target reactants, the n-undecane and n-dodecane sample bubblers were placed in a 70 °C hot bath to increase the vapor pressure of these compounds. Mass detection of both the target and reference reactants was achieved using a quadrupole mass spectrometer (Extrel MAX-1000) with an electron impact ion source. The mass spectrometer was housed in a vacuum chamber that was pumped by two 6-inch diffusion pumps with liquid nitrogen baffles, and the ultimate pressure of the chamber was less than 1 x 10-8 Torr. The target and reference compounds were ionized by bombardment of electrons with 40 eV of impact energy. Reactant ions were continuously sampled by the mass spectrometer from a twostage beam-inlet system. The target compounds and reference compounds were then detected by monitoring their molecular ion peaks, i.e., n-undecane was monitored at m/z = 156, n-dodecane at m/z = 170, and n-nonane, n-decane at m/z = 128, 142, respectively. There was essentially very little interference observed in mass spectral detection between target and reference compounds under our experimental conditions. Beam modulation in the second stage of the inlet system was accomplished by using a 200-Hz tuning fork chopper. Analog ion signals were directed to a lock-in amplifier (SR510) and the output analog signals were digitized by an analog to digital converter (Analog Devices RTI/815) and recorded by a personal computer. The mass spectral signals were found to be linearly proportional to the concentration of the compounds in the flow reactor.


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Assuming that both target and the reference compounds in the flow reactor were consumed by only with OH, Target (n-undecane or n-dodecane) + OH → products

(5)

Reference (n-nonane or n-decane) + OH → products

(6)

an integrated kinetics equation can be obtained as follows,21 [target],

ln [target]

,[]

[reference],

= ln [reference]

(I)

,[]

where [target]t,0 and [reference]t,0 were the concentrations of the target and reference compounds at a fixed reaction time t with absence of hydroxyl radicals, [target]t,OH and [reference]t,OH were the concentrations of target and reference compounds at t in the presence of hydroxyl radicals in the reactor. k5 and k6 represent the target and reference rate constants (in cm3 molecule-1 s-1) corresponding to reactions 5 and 6. Thus plotting ln([target]t,0/[target]t,OH) as a function of ln([reference]t,0/[reference]t,OH) is expected to yield a straight line with a slope equal to k5/k6, and the rate constant value for the reaction of the target compound with OH radical can then be calculated with a known reference rate constant k6 determined previously. By varying the temperature of the flow reactor the rate constant of reactions of OH with n-undecane and ndodecane as a function of temperature was then acquired. All kinetic measurements were repeated 3-5 times on different days to ensure consistency of kinetics data. Our experimental apparatus was also rearranged as shown in Figure 1b to assess the potential effects of secondary reactions on the kinetics results, which aimed at checking if the products from primary reactions 5 and 6 would contribute to the decay of reference and target compounds respectively. F2 (5% in 99.999% He) was obtained from Spectra Gases, Inc. Helium (99.999%) was obtained from Oxygen Service Company.

n-undecane (99%) and n-dodecane (99%) were

obtained from Acros Organics. n-nonane (99%) and n-decane (99.5%) were purchased from Alfa Aesar and Fisher Scientific, respectively. All chemicals were used as received. Deionized water was used as a precursor for the generation of OH radical via reaction 4.

Results And Discussion Figure 2 shows typical kinetics data for the reactions of OH radicals with n-undecane (Figure 2a) and n-dodecane (Figure 2b) at 298 K and a total pressure of 1 Torr using the 5 ACS Paragon Plus Environment


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RR/DF/MS technique with n-nonane and n-decane as reference compounds, respectively. It can be seen from Figure 2 that for a consumption of reactants up to 50%, the kinetics decay data followed the relationship described by equation (I). It was crucial that the decay of target and reference compounds was caused only by their reaction with OH radicals for accurate determination of the n-undecane and n-dodecane OH rate constants. There was a need to assess the effect of secondary reactions on the decay of target and reference compounds, in which the products generated from primary reactions 5 and 6 reacted with the reference and target compounds, contributing to the decay of these reactants. The assessment experiments were carried out using a modification of the RR/DF/MS arrangement as shown in Figure 1b, which allowed the primary products generated from reaction 5, mainly either n-C11H23 or n-C12H25, to react with the reference compounds, and the primary products produced from reaction 6, mainly either n-C9H19 or n-C10H21, to react with the target compounds. Results of the assessment experiments showed that the secondary reactions contributed to less than a 1% of the total decay of target and reference compounds. This suggested that the decay of the reactants in the present study was essentially unaffected by secondary reactions involving primary reaction products. In addition to the secondary reactions caused by primary reaction products, atomic hydrogen and oxygen produced from reactions in the flow reactor, OH + OH → H2O + O

(7)

O + OH → O2 + H

(8)

could also interact with the target and reference compounds to affect their decay. To assess the possible contribution of atomic H and O to the decay reactants, a model simulation using the Runge-Kutta method25 was carried out to calculate the concentration of target compounds and reference compounds by solving a series of differential rate equations defined by the chemical processes given in Table 1, in which the initial concentration of the reactants was assumed to be comparable to that used in the experiments. The results of these simulation calculations show that while the predicted concentration of the alkane loss were comparable to that observed in the experiment over a time interval of 30 ms, H and O atoms had little effect on the total decay of target and reference compounds, suggesting that the kinetics results obtained in the present work were not affected by reactions involving atomic hydrogen and atomic oxygen.


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A linear regression fit to all decay data points, acquired for n-undercane reaction with OH radicals at 298 K and a total pressure of 1 Torr, generated slope values of k5/k6 = 1.50 ± 0.04 and 1.15 ± 0.02 using n-nonane and n-decane as reference compounds respectively. With a literature value of kn-nonane+OH = (1.13±0.12) x 10-11 cm3 molecule-1 s-1 and kn-decane+OH = (1.29±0.11) x 10-11 cm3 molecule-1 s-1,23 the rate constant of OH reaction with n-undecane was determined to be knundecane+OH

= (1.70±0.19) x 10-11 and (1.48±0.14) x 10-11 cm3 molecule-1 s-1, respectively. Here the

cited uncertainties were taken as 2σ, which had taken into account the scattering of the kinetics data and the fluctuation of the experimental conditions, including pressure, temperature, and flow velocity. The average of these two values yielded kn-undecane+OH(298 K) = (1.59±0.24) x 10-11 cm3 molecule-1 s-1. For n-dodecane reaction with OH, slope values of 1.69±0.06 and 1.34±0.02 were produced also using n-nonane and n-decane as reference compounds at 298 K and a total pressure of 1 Torr, and the rate constant of OH reaction with n-dodecane was then determined to be kn-dodecane+OH = (1.90±0.21) x 10-11 and (1.75±0.15) x 10-11 cm3 molecule-1 s-1, respectively. The average of these two values yielded kn-dodecane+OH(298 K) = (1.83±0.26) x 10-11 cm3 molecule1

s-1. A summary of the rate constant of reactions of OH with n-undecane and n-dodecane are

given in Tables 2 and 3. The rate constant of OH reactions with n-undecane and n-dodecane were only measured using relative rate method by Zetzsch’s group (at 300 K by Behnke et al.19 and 312 K by Nolting et al.20) and rate constants of kn-undecane+OH(300 K) = (1.33±0.2) x 10-11 cm3 molecule-1 s-1 and kndodecane+OH(300

K) = (1.39±0.2) x 10-11 cm3 molecule-1 s-1 were reported.19 Our values of kn-

undecane+OH(298

K) = (1.59±0.24) x 10-11 cm3 molecule-1 s-1 and kn-dodecane+OH(298 K) = (1.83±0.26)

x 10-11 cm3 molecule-1 s-1 are 20% and 32% higher than that reported by Behnke et al. The difference between the present work and previous study could be due to the use of the OH rate constant of the reference compounds. Note that Behnke et al. used n-octane as the reference compound with kn-octane+OH(300 K) = 0.879 x 10-11 cm3 molecule-1 s-1, and the values of knnonane+OH

= (1.13±0.12) x 10-11 cm3 molecule-1 s-1 and kn-decane+OH = (1.29±0.11) x 10-11 cm3

molecule-1 s-1 used in the present work were slightly higher than the recommended values of knnonane+OH(298

K) = 0.970 x 10-11 cm3 molecule-1 s-1 and kn-decane+OH(298 K) = 1.10 x 10-11 cm3

molecule-1 s-1.31 In other words, the difference between our kinetics results and that reported by Behnke et al. would decrease to 2% and 12%, respectively if the recommended kn-nonane+OH(298 K) and kn-decane+OH(298 K) values were used in the present work. However, it was necessary to 7 ACS Paragon Plus Environment


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use the kn-nonane+OH and kn-decane+OH values from our previous measurements because these measurements provided the only temperature dependence of the reference rate constants for the present kinetics investigation of OH reactions with n-undecane and n-dodecane as a function of temperature. The rate constants of the reaction of OH with n-undecane and n-dodecane were also measured at 240 – 340 K at a total pressure of 1 Torr using both n-nonane and n-decane as references in the present work, and the results are also given in Tables 2 and 3. The average of the rate constants determined with two different references at corresponding temperature is listed in Table 4, and Figure 3 summarizes the temperature dependence of the OH rate constant of nundecane (Figure 3a) and n-dodecane (Figure 3b) using the information listed in Table 4. As shown in Figure 3, the rate constant of n-undecane and n-dodecane reactions with OH have two distinct regions of temperature dependence: a positive temperature dependence region at 277 K – 340 K, and a negative temperature dependent region at 277 – 240 K. This is unexpected since the reaction of OH with alkanes is known to be a hydrogen abstraction process associated with an activation energy barrier, which would require a rate constant to be positively dependent on temperature. In contrast to this understanding, the trend of negative temperature dependence of the rate constant at 240 K - 277 K appeared to be consistent for the reactions of OH with nundercane and n-dodecane when different reference compounds were used for measurements. For n-dodecane reaction with OH, rate constant was also measured at 245 K and 250 K, and the results indicated that the rate constant was not only negatively dependent on temperature but also in line with, in terms of the magnitude, the kinetics results at 240 K and 260 K, as shown in Figure 3b. The cause of the negative temperature dependence of the OH + n-undecane and ndodecane rate constants at 240 K – 277 K is unclear at this time, but we suspect that the water, which was used as the OH precursor in the present work, could play a role in this observation. It has been found that the water molecules can accelerate a reaction by forming complexes with the reactant through hydrogen bonding, which lowered the activation energy barrier of the chemical process.32 Since no similar precedent was found for the potential role of water in OH abstraction reactions we could now hypothesize that below 277 K n-undecane and n-dodecane molecules interacted with the water molecules to form intermediate n-alkane-water complexes through hydrogen bonding, i.e. n-C11H24•(H2O)n,

(n=1,2,…)

and n-C12H26•(H2O)n,


(n=1,2,…),

which distorted

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the molecular structure of the n-undecane and n-dodecane molecules. The molecular distortion due to complex with water molecules weakened the C-H bonds in the –CH2- groups of the nundecane and n-dodecane molecules, which further facilitated hydrogen abstraction by the OH radicals, making the H abstraction easier below 277 K than at 277 K. We also carried out kinetics measurements for the reactions of OH with n-undecane and n-dodecane at a total pressure of 1 – 5 Torr and 298 K with n-nonane as the reference compound in the present work, and our results indicated that the rate constant of these reactions were essentially pressure independent at 1 – 5 Torr, suggesting that the OH + n-undecane and ndodecane may not proceed via addition of OH radical to the n-alkanes, and that the high pressure limit had been reached at 1 Torr if these reactions involved formation of the intermediate nalkane-water complexes. On the other hand, Vu et al.33 discovered that the observed temperature dependence for the OH + hydroxyacetone reaction varied with pressure due to the formation of a pre-reactive complex, it is likely that the reactions of OH with n-undecane and n-dodecane might also vary with pressure at low temperatures if the reactions proceeded via formation of a prereactive complex. Figure 4 shows a summary of the OH + n-C6 – n-C12 alkane rate constant as a function of 1/T at 240 K – 340 K. It can be seen that at each temperature, the increase of carbon number in n-alkane associates with an increase of the OH rate constant value, reflecting the fact that more – CH2- sites are available in long chain n-alkane molecules than short chain n-alkane molecules for OH attack to extract the H atom. It is also observed from Figure 4 that for n-C6 – n-C9 alkanes, their OH rate constants are always positively dependent on temperature at 240 K – 340 K, as is expected. However, starting n-C10, the OH rate constant appeared to be negatively dependent on temperature at 240 K – 277 K, and the longer the carbon chain the more prominent the negative temperature dependence of the OH rate constant. This observation suggests that an additional mechanism was involved to accelerate the OH attack on n-undecane and n-dodecane at low temperatures. To the best of our knowledge, this trend has not been observed and studied previously. On the basis of our hypothesis above, the n-alkane molecules with a carbon chain of n > 12 is expected to react with OH faster below 277 K. More studies are needed to test this hypothesis, and a kinetics study of OH reactions with n-undecane and n-dodecane using an OH source without water as precursor would be desirable. An attempt using H + NO2 as the OH source to study the kinetics of the reactions of OH with n-undecane and n-dodecane in the 9 ACS Paragon Plus Environment


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present work was unsuccessful because the H + NO2 source could not produce enough OH radicals to produce measurable decays of the target and reference compounds, thus the absolute rate technique might be a better approach than the present technique to test the hypothesis with H + NO2 as the OH source. While the temperature dependent data for the n-dodecane system are convincing for the two different temperature regimes, the n-undecane data might be fit by a single regression. We tried to fit the n-undecande data by a single regression, and it was found that the single regression resulted in an overall negative temperature dependence behavior for the n-undecane + OH reaction, which would not correctly reflect our observation of the temperature behavior at 277 – 340 K. We therefore believed that there were two different temperature regimes for the reaction of n-undecane with OH. Since it is not possible to describe our kinetics results with a single Arrhenius equation, linear regression fits were separated in two different temperature regions to generate regression lines in the present work, which are shown in Figures 3a and 3b and summarized in Table 5. To be specific, Arrhenius expressions were found to be kn-undecane+OH = (6.58±2.60)×10-12exp[(238±102)/T] at 277 K – 340 K, and (2.29±0.95)×10-11exp[(-107±127)/T] at 277 K – 240 K, respectively. On the other hand, Arrhenius expressions were determined to be kn-dodecane + 11

OH

= (1.76±5.61)×10-14exp[(17872±795)/T] at 277 K – 340 K, and (3.59±0.77)×10-

exp[(-200±66)/T] at 260 K - 240 K, respectively. The only non-room temperature kinetics

study of the reactions of OH with n-undecane and n-dodecane was carried out by Nolting et al.20 who reported that kn-undecane+OH(312 K) = (1.36±0.03) x 10-11 and kn-dodecane+OH(312 K) = (1.50±0.05) x 10-11 cm3 molecule-1 s-1, respectively, using n-heptane as a reference, which are again lower than the projected rate constants at the corresponding temperature in the present work. Assuming that the OH radicals are primarily responsible for removal of these compounds from the atmosphere the lifetime, τ, of n-undecane and n-dodecane was estimated using: =

(10)

[]

where k277K is the OH rate constant of n-undecane and n-dodecane at 277 K, and [OH] is the average tropospheric OH concentration. Using [OH] = 8.1 × 105 molecules cm-3

34

and the

measured rate constants for n-undecane and n-dodecane at 277 K in the present work, the lifetimes of n-undecane and n-dodecane were estimated to be 25.8 and 19.8 hours, respectively.


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Summary In the present work, the RR/DF/MS technique has been used to determine the rate constant of the reactions of hydroxyl radicals with n-undecane and n-dodecane in a temperature of 240 K -340 K. Using n-nonane and n-decane as reference compounds, the average rate constant of OH + n-undecane and OH + n-dodecane was determine to be kn-undecane+OH(298 K) = (1.59±0.24) x 10-11 cm3 molecule-1 s-1 and kn-dodecane+OH(298 K) = (1.83±0.26) x 10-11 cm3 molecule-1 s-1, which is about 20% and 32% higher than that previously reported rate coefficients for the same reactions. The difference of our kinetics results could be due to the reference rate constants that were used to calculate the OH rate constant of the target compounds. The present work found that the rate constant of reaction of OH with n-undecane and ndodecane has two different temperature dependence regions in a temperature range of 240 K – 340 K: a positive temperature dependence at T ≥ 277 K, and a negative temperature dependence at T < 277 K. A review of the rate constant as a function of temperature for the reactions of OH with n-C6 – n-C12 alkanes indicates the negative temperature dependence phenomena below 277 K starts at n-C10, and the longer the chain length of the n-alkane, the more prominent this negative temperature dependence. It is hypothesized that at T < 277 K, complex of n-undecane and n-dodecane molecules water molecules causes structural distortion of the n-undecane and ndodecane molecule, which weakens the C-H bond of the –CH2- groups, allowing the hydrogen atom to be abstracted more easily by the OH radicals. While this hypothesis needs to be tested, our kinetics results indicate that the reaction of OH with n-undecane and n-dodecane can be faster temperature below 277 K, which could have a significant atmospheric implication in the troposphere where the temperature is below 277 K and the relative humidity is high. A relative humidity of 35% at 277 K corresponds to an absolute water vapor concentration of 7.4 x 1014 molecule cm-3 in the atmosphere,35 which is comparable to water concentration of 7.0 x 1014 molecule cm-3 used in the present work, thus under this atmospheric condition the contribution of n-undecane and n-dodecane to air pollution, such as photochemical smog and SOAs formation, may be accelerated.



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References: (1)

Cooke, J.A.;

Belluccia, M.; Mitchell D. Smooke, M.D.; Gomez, A.; Violi, A.;

Faravelli, T.; Ranzi, E. Computational and experimental study of JP-8, a surrogate, and its components in counterflow diffusion flames Proceedings of the Combustion Institute 2005, 30, 439–446. (2)

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(22) Crawford, M. A.; Dang, B.; Hoang, J.; Li, Z. Kinetic study of OH radical reaction with n-heptane and n-hexane at 240-340K using the relative rate/discharge flow/mass spectrometry (RR/DF/MS) technique Int. J. Chem. Kinet. 2011, 43, 489-497. (23) Li, Z., Singh, S., Woodward, W., Dang, L. Kinetics study of OH radical reactions with n-octane, n-nonane, and n-decane at 240-340 K using the relative rate/discharge flow/mass spectrometry technique J. Phys. Chem. A. 2006, 110, 12150 - 12157. (24) Sander, S. P.; Abbatt, J.; Barker, J. R.; Burkholder, J. B.; Friedl, R. R.; Golden, D. M.; Huie, R. E.; Kolb, C. E.; Kurylo, M. J.; Moortgat, G. Ket al. Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies, Evaluation No. 17. JPL Publication 10-6, Jet Propulsion Laboratory, Pasadena, 2011. (25) Steinfeld, J.I.; Francisco, J.S.; Hase, W.L. Chemical Kinetics and Dynamics, PrenticeHall, Inc. 2nd edition, 1998. (26) Arutyunov, V.S.; Buben, S.N.; Chaikin, A.M. Homogeneous and heterogeneous decay of oxygen and bromine atoms in the presence of molecular fluorine Kinet. Catal. 1979, 20, 465 - 469. (27) Zelenov, V.; Kukui, A.; Dodonov, A.; Aleinikov, N.; Kashtanov, S.; Turchin, A. Mass spectrometric determination of the rate constants of hydrogen atoms with fluorine molecules, xenon and krypton fluorides at 298-505 K. II. reaction of H + KrF2 Khim. Fiz. 1991, 10, 1121-1124. (28) Zellner, R.; Erler, K.; Field, D. Kinetics of the recombination reaction OH + H + M → H2O + M at low temperatures Symp. Int. Combust. Proc. 1977, 16, 939-948. (29) Cohen, N.; Westberg, K.R. Chemical kinetic data sheets for high-temperature reactions. Part II J. Phys. Chem. Ref. Data. 1991, 20, 1211-1311. (30) Holroyd, R.A.; Klein, G.W. Mercury-photosensitized decomposition of aliphatic hydrocarbons-radical detection with ethyl-carbon-14 radicals J. Phys. Chem. 1963, 67, 2273–2280. (31) Atkinson, R. Kinetics of the gas-phase reactions of OH radicals with alkanes and cycloalkanes. Atmos. Chem. Phys. 2003, 3, 2233 –2307. (32) Kumbhani, S.R.; Cline, T.S.; Killian, M.C.; Clark, J.; Hansen, L.D.; Shirts, R.B.; Robichaud, D.J.; Hansen, J.C. Water vapor enhancement of rates of peroxy radical reactions. Int. J. of Chem. Kinet. 2015, 47, 395 – 409. 14 ACS Paragon Plus Environment

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Table 1: List of Relevant Chemical Reactions Used in the Chemical Model Simulation in Assessing the Contribution of Atomic Oxygen and Hydrogen to the Decay of Target and Reference Compounds in RR/DF/MS Kinetic Data Analysis. k

Reactiona

3

(cm molecule-1 s -1)

Reference

F + H2O → HF + OH

1.40 x 10-11

24

OH + OH → H2O + O

1.80 x 10-12

24

OH + wall → product

10

Estimated -16

O + F2 → FO + F

1.00 x 10

FO + OH → O2 + HF

1.30 x 10-12 b

H + F2 → HF + F O + OH → O2 + H

24

1.38 x 10

-12

27

3.30 x 10

-11

24

10

H + wall → product

26

Estimated -31 c

28

-11 d

This work

-11 e

23

O + n-undecane → OH + other products

2.90 x 10

-13 f

29

O + n-nonane → OH + other products

2.10 x 10-13 f

29

3.42 x 10

-15 g

30

2.62 x 10

-15 g

30

2.30 x 10

H + OH + M → H2O + M

1.70 x 10

n-undecane + OH → products

1.13 x 10

n-nonane + OH → products

H + n-undecane → H2 + other products H + n-nonane → H2 + other products a

Initial concentrations are [H2O]0 = 7.0 x 1014, [OH]0 = 5.0 x 1013, [n-undecane]0 = 5.8 x 1013, [n-dodecane]0 = 5.6 x 1013, [nnonane]0 = 4.2 x 1013, and [n-decane]0 = 4.8 x 1013 molecules cm-3, respectively. All other initial concentrations are set to 0.

b

Estimation was based on k(ClO + OH).

c

The unit is cm6 molecule-2 s-1

d e

-11

cm3 molecule-1 s -1 for n-dodecane + OH.

-11

cm3 molecule-1 s -1 for n-decane + OH.

k = 1.90 x 10

k = 1.29 x 10

f

Estimate based on the O + n-C8H18 rate constant.

g

Estimate based on the H + n-C8H18 rate constant.


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Table 2: Summary of n-Undecane + OH Rate Constants at 240 – 340 K. k

Temperature (K)

Reference Compound

Slope

340

n-Decane

1.01 ± 0.03b (20)c

320

n-Decane

298

Techniquea

Reference

1.46 ± 0.16

RR/DF/MS

This Work

1.08 ± 0.04 (22)

1.54 ± 0.16

RR/DF/MS

This Work

n-Decane

1.15 ± 0.02 (87)

1.48 ± 0.14

RR/DF/MS

This Work

277

n-Decane

1.17 ± 0.02 (45)

1.43 ± 0.13

RR/DF/MS

This Work

260

n-Decane

1.29 ± 0.02 (50)

1.56 ± 0.17

RR/DF/MS

This Work

240

n-Decane

1.45 ± 0.02 (35)

1.76 ± 0.15

RR/DF/MS

This Work

340

n-Nonane

1.35 ± 0.05 (22)

1.80 ± 0.26

RR/DF/MS

This Work

320

n-Nonane

1.60 ± 0.05 (19)

1.85 ± 0.25

RR/DF/MS

This Work

298

n-Nonane

1.50 ± 0.04 (25)

1.70 ± 0.19

RR/DF/MS

This Work

277

n-Nonane

1.70 ± 0.06 (18)

1.65 ± 0.20

RR/DF/MS

This Work

260

n-Nonane

2.03 ± 0.07 (17)

1.78 ± 0.23

RR/DF/MS

This Work

240

n-Nonane

2.19 ± 0.07 (17)

1.76 ± 0.19

RR/DF/MS

This Work

312

n-Heptane

-

1.37 ± 0.03

RR

20

300

n-Octane

-

1.33 ± 0.02

RR

19

(10

-11

3

-1 -1

cm molecule s )

a

RR/DF/MS: Relative Rate/Discharge Flow/Mass Spectrometry, RR: Relative Rate.

b

all uncertainties were taken to be 2σ.

c

numbers in parentheses represent the number of data point collected.



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Page 18 of 26

Table 3: Summary of n-dodecane + OH Rate Constant at 240 – 340 K. Temperature

Reference

k Slope

Techniquea

Reference

(K)

Compound

340

n-Decane

1.28 ± 0.02b (27)c

1.85 ± 0.17

RR/DF/MS

This Work

320

n-Decane

1.43 ± 0.03 (21)

2.03 ± 0.18

RR/DF/MS

This Work

298

n-Decane

1.34 ± 0.02 (103)

1.75 ± 0.15

RR/DF/MS

This Work

277

n-Decane

1.41 ± 0.02 (28)

1.72 ± 0.15

RR/DF/MS

This Work

260

n-Decane

1.50 ± 0.02 (25)

1.82 ± 0.20

RR/DF/MS

This Work

250

n-Decane

1.68 ± 0.08 (18)

2.00 ± 0.29

RR/DF/MS

This Work

245

n-Decane

1.95 ± 0.08 (18)

2.29 ± 0.26

RR/DF/MS

This Work

240

n-Decane

2.35 ± 0.06 (44)

2.85 ± 0.28

RR/DF/MS

This Work

340

n-Nonane

1.57 ± 0.05 (25)

2.09 ± 0.28

RR/DF/MS

This Work

320

n-Nonane

1.62 ± 0.04 (27)

1.88 ± 0.25

RR/DF/MS

This Work

298

n-Nonane

1.69 ± 0.06 (62)

1.90 ± 0.21

RR/DF/MS

This Work

277

n-Nonane

1.81 ± 0.04 (31)

1.75 ± 0.19

RR/DF/MS

This Work

260

n-Nonane

2.02 ± 0.03 (38)

1.78 ± 0.21

RR/DF/MS

This Work

250

n-Nonane

2.48 ± 0.11 (10)

2.08 ± 0.30

RR/DF/MS

This Work

245

n-Nonane

3.34 ± 0.14 (8)

2.72 ± 0.34

RR/DF/MS

This Work

240

n-Nonane

4.50 ± 0.12 (29)

3.61 ± 0.40

RR/DF/MS

This Work

300

n-Octane

-

1.39 ± 0.02

RR

19

312

n-Heptane

-

1.50 ± 0.05

RR

20

(10

-11

3

-1 -1

cm molecule s )

a

RR/DF/MS: Relative Rate/Discharge Flow/Mass Spectrometry, RR: Relative Rate.

b

all uncertainties were taken to be 2σ.

c

numbers in parentheses represent the number of data point collected.


Page 19 of 26

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Table 4. Average rate constant of OH reaction with n-undecane and n-dodecane at 240 – 340 K determined using the RR/DF/MS technique in the present work. Temperature

n-undecane + OH

Temperature

n-dodecane + OH

(K)

(10-11 cm3 molecule -1 s-1)

(K)

(10-11 cm3 molecule -1 s-1)

340

1.63 ± 0.31

340

1.97 ± 0.33

320

1.70 ± 0.30

320

1.96 ± 0.31

298

1.59 ± 0.24

298

1.83 ± 0.26

277

1.54 ± 0.24

277

1.74 ± 0.24

260

1.67 ± 0.29

260

1.80 ± 0.29

240

1.76 ± 0.24

250

2.04 ± 0.42

245

2.51 ± 0.43

240

3.23 ± 0.49



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Page 20 of 26

Table 5. Summary of Arrhenius expression of the reaction of OH with n-undecane and ndodecane. OH + n-undecane Temperature (K)

a

OH + n-dodecane

A

A

(K)

(cm3 molecule -1 s-1)

(K)

(cm3 molecule -1 s-1)

240 – 277

(2.29 ± 0.95) x 10-11

-107 ± 127

(3.59 ± 0.77) x 10-11 a

-200 ± 66

277 – 340

(6.58 ± 2.60) x 10-12

238 ±102

(1.53 ± 5.64) x 10-14

1787 ± 795

T = 240-260 K


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Figure captions Figure 1. RR/DF/MS experimental apparatus for kinetic studies of gas phase reactions of OH with n-undecane and n-dodecane (a), and the rearrangement of the flow reactor (b) for checking potential effects of secondary reactions on kinetics results. Figure 2. Typical kinetics data for n-undecane + OH using n-nonane and n-decane as reference compounds (a), and for n-dodecane + OH using n-nonane and n-decane as reference compounds (b). Initial concentrations are: [F2]0 = (0 - 3.5) x 1013, [H2O]0 = 7.0 x 1014, [n-undecane]0 = 8.2 x 1013, [n-dodecane]0 = 5.7 x 1013, [n-nonane]0 = 4.4 x 1013 molecules cm-3, and [n-decane]0 = 4.6 x 1013, respectively. Figure 3. Arrhenius plot for the n-undecane + OH (a) and n-dodecane + OH (b) at 240 – 340 K and 1 Torr along with available experimental data from literature. The black line is derived from a regression of the data at 277 – 340 K, and the red line represents a regression of the data at 277 – 240 K in (a) and at 260 – 240 K in (b), respectively. Figure 4. Summary of the rate constant of OH + n-alkane (n = 6 – 12) as a function of temperature using the RR/DF/MS technique.



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Figures Figure 1.

(a)

(b)


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Page 23 of 26

ln([n-undecane]t,0 / [n-undecane]t,[OH])

Figure 2.

1.0 Reference: n-decane Reference: n-nonane 0.8

P = 1.0 - 1.1 Torr Total T = 298 K 0.6

(a)

0.4

0.2

0.0 0.0

0.2

0.4

0.6

0.8

ln([reference]t,0 / [reference]t,[OH])

ln([n-dodecane]t,0 / [n-dodecane]t,[OH])

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1.0 Reference: n-decane Reference: n-nonane 0.8

P

= 1.0 - 1.1 Torr Total T = 298 K

0.6

0.4

(b)

0.2

0.0 0.0

0.1

0.2

0.3

0.4

0.5

ln([reference]t,0 / [reference]t,[OH])


0.6


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3.

(a)

(b)


Page 24 of 26

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Figure 4.



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TOC Graphic


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Kinetics Study of the Reactions of OH with n ... - ACS Publications

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