(Z

Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE

A: Kinetics and Dynamics

Rate Constants for the Reactions of OH Radical with the (E)/(Z) Isomers of CFCF=CHCl and CHFCF=CHCl 3

2

Kazuaki Tokuhashi, Tadafumi Uchimaru, Kenji Takizawa, and Shigeo Kondo J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.7b11923 • Publication Date (Web): 07 Mar 2018 Downloaded from http://pubs.acs.org on March 7, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 41 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

The Journal of Physical Chemistry

Rate Constants for the Reactions of OH Radical with the (E)/(Z) Isomers of CF3CF=CHCl and CHF2CF=CHCl

Kazuaki Tokuhashi, Tadafumi Uchimaru, Kenji Takizawa*, Shigeo Kondo

National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan

*Corresponding

author:

Kenji

Takizawa

([email protected],

Tel:

+81-29-861-9441, FAX: +81-29-861-4770)

Short Title: Rate Constant for OH with CF3CF=CHCl and CHF2CF=CHCl Isomers

1 ACS Paragon Plus Environment

The Journal of Physical Chemistry 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

Page 2 of 41

Abstract The rate constants for the reactions of OH radical with (E)- and (Z)-isomers of CF3CF=CHCl and CHF2CF=CHCl have been measured over the temperature range of 250–430 K. Kinetic measurements have been performed using flash and laser photolysis methods combined with laser induced fluorescence. Arrhenius rate constants

have

been

determined

(1.09±0.03)×10-12·exp[(50±10)K/T],

as

k((E)-CF3CF=CHCl)

k((Z)-CF3CF=CHCl)

= =

(8.02±0.19)×10-13·exp[-(100±10)K/T], k((E)-CHF2CF=CHCl) = (1.50±0.03)×10-12 ·exp[(160±10)K/T], and k((Z)-CHF2CF=CHCl) = (1.36±0.03)×10-12·exp[(360±10)K/T] cm3 molecule-1 s-1. Infrared absorption spectra have also been measured at room temperature. The atmospheric lifetimes of (E)-CF3CF=CHCl, (Z)-CF3CF=CHCl, (E)-CHF2CF=CHCl, and (Z)-CHF2CF=CHCl have been estimated as 8.9, 20, 4.6, and 2.6 days, respectively, and their global warming potentials and ozone depletion potentials were determined as 0.23, 0.88, 0.060, and 0.016 and 0.00010, 0.00023, 0.000057, and 0.000030, respectively. Additionally, the rate constants for OH radical addition and IR spectra of these compounds were determined computationally. Consistent with experiment, our calculations indicate that the reactivity toward OH radical addition is reduced as (Z)-CHF2CF=CHCl > (E)-CHF2CF=CHCl > (E)-CF3CF=CHCl > (Z)-CF3CF=CHCl, where the (E)/(Z) reactivity is reversed for CF3CF=CHCl and CHF2CF=CHCl. The calculations reproduced the observed


Page 3 of 41 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


temperature dependencies of the rate constants for the OH radical reactions, which is slightly positive for (Z)-CF3CF=CHCl but negative for the other compounds.



1. Introduction Hydrochlorofluoroalkenes (HCFOs) such as (E)-CF3CH=CHCl have been developed as alternatives to chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs) due to their very short atmospheric lifetimes. However, these compounds have been shown to contribute to global warming when released to the atmosphere since the C-F bond absorbs infrared light of the solar spectrum. In addition, because HCFOs contain a chlorine atom, these compounds may contribute to the depletion of the stratospheric ozone layer by decomposing and releasing chlorine atoms in the stratosphere. The global warming potential (GWP) depends on the decomposition rate in the atmosphere or the atmospheric lifetime and the infrared absorption intensities. Because the main decomposition pathway of halogenated alkenes is their reaction with OH radicals, the atmospheric lifetime can be obtained from their corresponding reaction rates. Further, the ozone depletion potential (ODP) also depends on the atmospheric lifetimes. Therefore, it is indispensable to evaluate the reaction rates of halogenated alkenes with OH radicals and their infrared spectra. In this work, we measured the reaction rate constants of (E)-CF3CF=CHCl, (Z)-CF3CF=CHCl, (E)-CHF2CF=CHCl, and (Z)-CHF2CF=CHCl with the OH radical over the temperature range 250–430 K. We estimated the atmospheric lifetimes of CF3CF=CHCl and CHF2CF=CHCl isomers with respect to their reaction with OH


Page 4 of 41

Page 5 of 41 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


radical, and consequently their ozone depleting potential (ODP). We have also measured the infrared absorption spectra of the two isomers. From the atmospheric lifetimes and infrared absorption spectra, the GWPs were then estimated. Our experimental measurements indicated that the difference in (E)/(Z) reactivity of CH3CF=CHCl with the OH radical was reversed relative to that of CHF2CF=CHCl (see Section 3.4.2.). To investigate these trends in (E)/(Z)-reactivity more fully, computational techniques were employed to calculate the rate constants for the OH radical reactions. Furthermore, the IR spectra of the (E)- and (Z)-isomers of CF3CF=CHCl and CHF2CF=CHCl were also calculated.



2. Experimental The experimental apparatus and procedure for the kinetic measurements have been described in detail elsewhere.1,2 Briefly, the kinetic measurements were performed under pseudo-first-order reaction conditions with a large excess of the sample (CF3CF=CHCl or CHF2CF=CHCl isomers) relative to the initial concentration of OH radicals produced by using either the flash photolysis (FP) or laser photolysis (LP) method. The initial concentration of OH radicals for the FP and LP methods was estimated previously;25 it was kept smaller than 1×1011 molecule cm-3 in the present study. In the case of the FP method, H2O was directly photolyzed with pulsed light using a Xe flash lamp (EG & G, FX-193U, 600–1300V, 2 µF, pulse energy: 0.36–1.69 J pulse-1, usually 0.64 J pulse-1, pulse width: 10–20 µs, λ≥180 nm, quartz cut-off) in the presence of a large excess of argon bath gas. In the case of the LP method, two approaches were considered. Firstly, OH radicals were produced by the reaction O(1D) + H2O → 2OH (LP-H2O method), where O(1D) atoms were generated by photo-dissociation of N2O using an ArF excimer laser (Coherent, ExciStar XS) with λ=193 nm. Secondly, OH radicals were produced by the reaction O(1D) + CH4 → OH + CH3, which was used as a water-free OH production method (LP-CH4 method). The power density of the excimer laser at the exit window of the reaction cell was ~2–5 mJ cm-2 pulse-1. In the case of the LP method, helium was used as the bath gas. In order to prevent accumulation of photofragments and/or reaction products, all experiments


Page 6 of 41

Page 7 of 41 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


were carried out under slow-flow conditions over the total pressure range 5–200 Torr. The repetition rate of the flash lamp and excimer laser was set at 10 Hz. The OH radical concentration was monitored using the laser induced fluorescence (LIF) technique. The excitation light for the LIF method originated from a frequency doubled tunable dye laser (Quantel, TDL90) pumped by the second harmonic of a Nd:YAG laser (λ=532 nm, 10 Hz), and the wavelength was tuned at λ=308 nm. A photo-multiplier tube was used to monitor the fluorescence signal from OH radicals. The signals were detected by the photon-counting technique and were counted and accumulated using a multi-channel scaler/averager (Stanford, SR430). The signals were stored in a microcomputer for further data processing. The mass flow rates were controlled and measured using calibrated mass flow controllers (MKS Type1259). The total gas pressure of the reactor was measured by a capacitance manometer (MKS Type 626A). The temperature of the reactor was maintained either by an electric heater or by circulating fluid around the outer jacket of the reactor from a temperature controlled bath, which was monitored with a Type K thermocouple (CHINO). During the experiments, the temperature across the reaction volume was maintained within ±2 K of the target temperature over the temperature range examined. In order to ensure that the experimental data are free from any systematic errors, the experiments were repeated at intervals from several days to several months under a variety of experimental conditions (e.g., total pressure of 5–



200 Torr, Ar bath gas for the FP method, and He bath gas for the LP-H2O and LP-CH4 methods). CF3CF=CHCl and CHF2CF=CHCl isomers were obtained from Asahi Glass Co., Ltd. Their purity was determined using a GC-FID (Shimadzu, GC-2014 and GC-14B), and the integrated area of the main peak relative to the total area was taken as the sample purity. The analysis was carried out using various columns, with the lowest value used to signify the sample purity. The purities of the original samples of (E)-CF3CF=CHCl, (Z)-CF3CF=CHCl, (E)-CHF2CF=CHCl, and (Z)-CHF2CF=CHCl were approximately 70% (main impurity was ~30% of Z-isomer), 89.5% (main impurity was 10.1% of E-isomer), 92.9% (main impurity was 6.4% of Z-isomer), and 97.9% (main impurity was 1.8% of E-isomer), respectively. Note that the individual impurities were not identified. The samples were further purified by gas chromatography and the purified sample purities were 99.4% (Z-isomer was 0.01%), 99.92% (E-isomer was 0.003%), 99.99% (Z-isomer was 0.001%), and 99.98% (E-isomer was 0.006%) for (E)-CF3CF=CHCl, (Z)-CF3CF=CHCl, (E)-CHF2CF=CHCl, and (Z)-CHF2CF=CHCl, respectively. Measurements of the reaction rate constants with OH radical and the IR absorption have been carried out using the purified samples. The IR spectra were measured with a FTIR (Shimadzu FTIR-8700) with the following conditions: IR cell, 10 cm long; KBr; window resolution, 1 cm-1;


Page 8 of 41

Page 9 of 41 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


wavenumber range, 4000–400 cm-1; integration, 50 times; bath gas N2; total pressure 760 Torr. Because FTIR tends to show significantly large absorption peaks due to H2O and CO2 under ambient conditions, dry nitrogen was allowed to flow into the optical path region to purge H2O and CO2; the influence of their absorption was not apparent after subtracting the background spectrum.



3. Results and Discussion 3.1. Kinetic Measurements Rate constants for the reaction of OH radical with CF3CF=CHCl and CHF2CF=CHCl isomers were measured over the temperature range of 250–430 K. Examples of a decay plot for the OH radical and a plot of the observed pseudo-first-order rate constant kobs against (Z)-CF3CF=CHCl concentration are shown in the Supporting Information (SI, Figure S1). Since the OH radical decay plots show linear relationship, the pseudo-first-order rate constant (kobs) can be derived from the slopes of the straight lines by least squares fit to each decay plot. As shown in the inset of Figure S1, the plot of the pseudo-first-order rate constant versus (Z)-CF3CF=CHCl concentration is distributed along a straight line with little scatter, and the rate constant for the reaction of OH radical with (Z)-CF3CF=CHCl can be derived from the slope by the linear least squares fit to the observed data. The intercept of kobs versus (Z)-CF3CF=CHCl concentration for zero reactant (kd) is attributed to the diffusion of OH radicals from the viewing zone, and is partially caused by the reaction of OH radical with impurities contained in the gas mixture. The kd was dependent on the experimental conditions. For each data set of the plot of kobs versus reactant concentration for various experimental conditions, the value of kd was subtracted from kobs. Figure S2 in the SI shows pseudo-first-order rate constants corrected for background value (kobs - kd)


Page 10 of 41

Page 11 of 41 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


versus (Z)-CF3CF=CHCl concentration for various temperature conditions. The plots exhibit linearity with relatively little scatter. In all cases, the OH radical decay shows exponential behavior, and the linearity and the scatter of the plotted data for individual experiments are very similar to those shown in Figure S1. Additionally, the degree of linearity and the scatter of kobs - kd versus reactant concentration is similar to those shown in Figure S2. The obtained rate constants and detailed information about the experimental conditions are provided shown in the SI (Tables S1–S4). Here, the error limits are at the 95% confidence level, as derived from the linear least squares fit to the plot of the first order rate constant versus reactant concentration. Note that systematic errors are not considered, which in our experiments are estimated to be less than ±10%. Rate constants were found to be independent of pressure in the temperature range shown in Tables S1–S4, within the experimental errors. Arrhenius plots are shown in Figure 1. As can be seen in Figure 1, the Arrhenius plots give linear relationships in the temperature range examined. The differences among the results obtained by the different methods are small. Thus, it is concluded that the systematic errors among the individual experimental techniques as well as any systematic errors are negligible. Non-Arrhenius behavior was not evident, which in any event would be within the error limits of these experiments. Therefore, the rate constants obtained in this study were fit to the Arrhenius rate expression. Table 1 lists the Arrhenius rate parameters for the



Page 12 of 41

CF3CF=CHCl and CHF2CF=CHCl isomers. The rate constants at T=298 K derived from the Arrhenius rate parameters are also listed in Table 1. There are no previously reported values of the rate constants for the reaction of OH radicals with the CF3CF=CHCl and CHF2CF=CHCl isomers.

3.2. Measurement of IR Absorption Spectra The infrared absorption spectra of the CF3CF=CHCl and CHF2CF=CHCl isomers between 400–2500 cm-1 at approximately 298 K in 760 Torr of N2 are shown in Figure 2. The infrared spectra of (E)-CF3CF=CHCl, (Z)-CF3CF=CHCl, (E)-CHF2CF=CHCl, and (Z)-CHF2CF=CHCl measured over the partial pressure range of 1.4–3.2, 2.1–3.9, 1.5–4.8, and 1.6–5.7 Torr, respectively, obeyed the Beer–Lambert's law. Infrared absorption band strengths for the CF3CF=CHCl and CHF2CF=CHCl isomers and the digitized infrared spectra are available in Table S5 of the SI. Infrared absorption band strengths

integrated

between

470–2000

cm-1

were

(1.714±0.015)×10-16,

(1.790±0.025)×10-16, (1.097±0.026)×10-16, and (1.016±0.040)×10-16 cm2 molecule-1 cm-1

for

(E)-CF3CF=CHCl,

(Z)-CF3CF=CHCl,

(E)-CHF2CF=CHCl,

and

(Z)-CHF2CF=CHCl , respectively. Here, the error limits are 95% confidence level from the integrated absorption cross sections of an individual spectrum with different concentrations (6–8 spectra). Comparison with previously reported IR absorption spectra of CF3CF=CHCl and CHF2CF=CHCl isomers is not possible as none are


Page 13 of 41 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


available.

3.3. Atmospheric Implications Using the rate constants measured in this study, the atmospheric lifetimes of the CF3CF=CHCl and CHF2CF=CHCl isomers with respect to reaction with the OH radical have been estimated from a global tropospheric 24 h average OH radical concentration (1×106 radicals cm-3, as reported by Prinn et al.3) and the rate constants at T=298 K derived from the Arrhenius rate parameters listed in Table 1. The estimated lifetimes of the CF3CF=CHCl and CHF2CF=CHCl isomers are provided in Table 2. Radiative efficiencies (RE) for the CF3CF=CHCl and CHF2CF=CHCl isomers were estimated using the infrared spectra measured in this work using a method based on the well-mixed model reported by Hodnebrog et al.4 The RE for (E)-CF3CF=CHCl, (Z)-CF3CF=CHCl, (E)-CHF2CF=CHCl, and (Z)-CHF2CF=CHCl were estimated to be 0.241, 0.216, 0.195, and 0.148 W m-2 ppb-1, respectively, using a 1 cm-1 resolution model. By comparison, the instantaneous forcings (IF) of these compounds were estimated to be 0.253, 0.226, 0.204, and 0.155 W m-2 ppb-1, respectively, using the 10 cm-1 resolution model reported by Pinnock et al.5 As seen, the RE of the four compounds studied in this work were approximately 5% smaller than the IF values. The difference between RE and IF seems to be caused by the distinct spectral resolutions and radiative forcing efficiencies.



Hodnebrog et al.4 reported a method for estimating the radiative efficiency of very short-lived compounds based on a lifetime correction (Eq. (2) and SI of Hodnebrog et al.). To this end, the radiative efficiencies as well as their corresponding lifetime-corrected radiative efficiencies are listed in Table 2. Relative to those calculated by the well-mixed model, the lifetime-corrected radiative efficiencies were decreased by factors of 0.094, 0.18, 0.052, and 0.031 for (E)-CF3CF=CHCl, (Z)-CF3CF=CHCl, (E)-CHF2CF=CHCl, and (Z)-CHF2CF=CHCl, respectively. The global warming potentials for the 100 year time horizon (GWP100) using the lifetime-corrected radiative efficiencies are calculated using the approach outlined in the Supporting Information of Hodnebrog et al.4 and are listed in Table 2. GWP100 values of the CF3CF=CHCl and CHF2CF=CHCl isomers estimated in this study are smaller than 1, and the influence of these compounds on climate change seems to be negligible. By comparison, GWP100 values estimated using the well-mixed model developed by Pinnock et al.5 are 2.5, 5.3, 1.2, and 0.5 for (E)-CF3CF=CHCl, (Z)-CF3CF=CHCl, (E)-CHF2CF=CHCl, and (Z)-CHF2CF=CHCl, respectively. Patten and Wuebbles6 evaluated the ozone depleting potential (ODP) of (E)-CF3CH=CHCl using a 3-D atmospheric model with the OH radical reaction rate constant of 4.4×10-13 cm3 molecule-1 s-1 at T=295 K measured by Sulbaek Andersen et al.7 They reported an ODP of 0.00034 for (E)-CF3CH=CHCl. Gierczak et al.8 and Orkin et al.9 reported a temperature-dependent OH radical reaction rate constant for


Page 14 of 41

Page 15 of 41 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


(E)-CF3CH=CHCl, and Burkholder et al.10 recommended a OH radical rate constant of k((E)-CF3CH=CHCl) = 9.0×10-13·exp[-280K/T] for (E)-CF3CH=CHCl. The OH radical reaction rate constant of (E)-CF3CH=CHCl reported by Sulbaek Andersen et al.7 seems to be slightly higher than those reported by Gierczak et al.8 and Orkin et al.9 According to the recommended OH radical rate constant of (E)-CF3CH=CHCl by Burkholder et al.,10 the OH radical rate constant at T=272 K becomes 3.22×10-13 cm3 molecule-1 s-1, which is approximately 27% smaller than the OH radical rate constant at T=295 K (4.4×10-13 cm3 molecule-1 s-1) reported by Sulbaek Andersen et al.7 As mentioned by Gierczak et al.,8 the ODP does not change linearly against lifetime; therefore, model calculations would be required to evaluate the ODP. However, the ability to estimate the ODP by a simple procedure also seems to be valuable. Orkin et al.9 reported that the OH radical rate constant reported by Sulbaek Andersen et al. 7 was ~47% larger than their value at T=272 K, and they reported 0.00050 as a modified ODP based on the difference in the rate constants. We applied the same correction for the difference in the rate constants to yield an ODP for (E)-CF3CH=CHCl of 0.00047. Using the corrected ODP of (E)-CF3CH=CHCl, we estimated the ODPs of the CF3CF=CHCl and CHF2CF=CHCl isomers based on the following simple scaling procedure: ODP = ODP1233zdሺாሻ

ெ௪1233xdሺಶሻ ெ௪

ఛ

௡

ఛ1233zdሺಶሻ ௡1233zdሺಶሻ

(1)

where Mw, τ, and n are the molecular weight, lifetime, and number of Cl atoms



Page 16 of 41

contained in the compound, respectively, and the subscript 1233zd(E) is (E)-CF3CH=CHCl. The results are listed in Table 2. As seen, the ODP of the CF3CF=CHCl

and

CHF2CF=CHCl

isomers

are

less

than

half

that

of

(E)-CF3CH=CHCl, and their contribution to stratospheric ozone depletion is expected to be negligible. Recently, Wallington et al.24 studied the atmospheric lifetimes, photochemical ozone creation potentials (POCPs), GWPs, and ODPs of the short-chain haloolefins CF3CF=CH2,

(Z)-CF3CH=CHF,

CF3CF=CF2,

(Z)-CF3CH=CHCl,

and

(E)-CF3CH=CHCl. They reported that these short-chain haloolefins have short atmospheric lifetimes, negligible POCPs, GWPs, and ODPs, and are environmentally benign. The results of the present study are consistent with the results of Wallington et al.24

3.4. Computational Results Computational techniques were employed to estimate the (E)/(Z) energy differences of CF3CF=CHCl and CHF2CF=CHCl. The differences in the kinetic behavior and IR spectra between these (E)/(Z) isomers were also characterized through computational investigations. All calculations were performed using the Gaussian software package.11


Page 17 of 41 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


3.4.1. Structures of the (E)- and (Z)-isomers and their energy differences To locate the minimum energy structures of the (E)- and (Z)-isomers of CF3CF=CHCl and CHF2CF=CHCl, we examined the energy profiles for rotation of their CF3 or CHF2 groups. Calculations were performed using the M06-2X density functional12,13 in conjunction with the aug-cc-pVTZ basis set.14,15 The calculated rotational energy profiles are shown in Figures S3 and S4. The global minimum energy structures of the (E)- and (Z)-isomers of CF3CF=CHCl possess Cs symmetry, in which one of the C-F bonds in the CF3 group is eclipsed to the C-C double bond (Figure

S3).

Correspondingly,

the

global

minimum

energy

structure

of

(E)-CHF2CF=CHCl has a Cs symmetry plane on which the C-H bond in the CHF2 group is located. Meanwhile, the (Z)-isomer of CHF2CF=CHCl has two distinct energy minima. The dihedral angle of the C=C-C-H moiety is ~120° and 0° in the global minimum energy structure (C1 symmetry) and in the second lowest minimum energy structure (Cs symmetry), respectively (Figure S4). The energy profiles shown in Figures S3 and S4 indicate that the (Z)-isomer is lower in energy than the (E)-isomer for both CF3CF=CHCl and CHF2CF=CHCl. To obtain more accurate (E)/(Z) energy differences for CF3CF=CHCl and CHF2CF=CHCl, sophisticated ab initio calculations were also performed (see the SI). The calculated values of the (E)/(Z) energy differences for CF3CF=CHCl and CHF2CF=CHCl, as well as the energy difference between the global minimum energy and the second lowest



minimum energy structures of (Z)-CHF2CF=CHCl are listed in Table S6. The (E)/(Z) energy difference is found to be larger for CF3CF=CHCl (∆H(298 K) = 3.8 kcal/mol) than for CHF2CF=CHCl (∆H(298 K) = 1.6 kcal/mol). This result can be attributed to the fact that the CF3 group is bulkier than the CHF2 group. That is, Taft’s Es values of the CF3 and CHF2 groups are -1.16 and -0.67, respectively, with more negative values of Es indicating a larger steric effect.16 Hence, the interaction between the CF3 group and the chlorine atom in the (E)-isomer of CF3CF=CHCl will be relatively more repulsive and exhibit a stronger destabilizing effect than that between the CHF2 group and the chlorine atom in the (E)-isomer of CHF2CF=CHCl. The energy difference between the global and the second lowest energy minima of (Z)-CHF2CF=CHCl is smaller (∆H(298 K) = 0.5 kcal/mol) than its (E)/(Z) energy difference (Table S6).

3.4.2. Kinetics of OH radical addition to CF3CF=CHCl and CHF2CF=CHCl Research groups of Rajakumar et al.17–19 and Zhang et al.20 have recently reported computational results on the reactions of halogenated alkenes with OH radicals. The authors concluded that the reactions predominantly proceed via the addition of OH radical to the C-C double bond rather than direct hydrogen atom abstraction. The contribution of the hydrogen atom abstraction pathways was found to be negligible in the temperature range of 200–400 K. Fluorinated alkenes possessing hydrogen atom(s) at the allylic position are likely to be particularly reactive toward hydrogen abstraction.


Page 18 of 41

Page 19 of 41 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


Nevertheless, even for such fluorinated alkenes, more specifically for (E)- and (Z)CHF=CHCHF2 and CF2=CHCHF2, Ramanjaneyulu and Rajakumar19 have shown that the calculated rate of hydrogen abstraction is one or two orders of magnitude smaller than that of the addition of OH radical. Considering these reports, the contribution of hydrogen abstraction pathways are also likely to be insignificant for CF3CF=CHCl and CHF2CF=CHCl within the temperature range of 250–430 K, and the rates of the addition pathways must be predominant for determining the trends in (E)/(Z) reactivity of these alkenes. We thus focus our computational investigation on the OH radical addition to the C-C double bonds in the (E)/(Z) isomers of CF3CF=CHCl and CHF2CF=CHCl. The geometries of the reactants and the transition states for OH radical addition were optimized using the M06-2X exchange–correlation functional12,13 in conjunction with the aug-cc-pVTZ basis set.14,15 To better evaluate the energies of the stationary points, single-point-energy CCSD(T)21 calculations with the aug-cc-pVTZ basis set were also performed. The detailed procedure for computing the rate constants for the OH radical addition is described in the Supporting Information. Addition of the OH radical will occur at the terminal ends and the central carbon atoms in CF3CF=CHCl and CHF2CF=CHCl. We located the transition states for both reaction channels. The calculated energies of the transition states relative to the reactants are listed in Table S7. It should be noted that the transition states for OH



radical addition to the central carbon atoms are lower in energy than the analogous transition states for addition to the terminal carbon atoms. The incipient radical centers in the former transition states likely experience relatively large stabilization effects by the neighboring chlorine atom. Accordingly, the rates for OH radical addition to the central carbon atoms are markedly larger than that for addition to the terminal carbon atoms (Table 3). The calculated total rate constants for OH radical addition are given in Table 3, and their Arrhenius plots are compared with those determined experimentally in Figure S5. The calculated rate constants are in reasonable agreement with the experimental values. Experimentally observed reactivity trends are reproduced in our computational results on the following points. (i) The reactivity toward OH radical addition is reduced in the order of (Z)-CHF2CF=CHCl > (E)-CHF2CF=CHCl > (E)-CF3CF=CHCl > (Z)-CF3CF=CHCl in the temperature range of 250–430 K. The (E)/(Z) reactivity is reversed for CF3CF=CHCl and CHF2CF=CHCl; that is, the (E)-isomer shows higher reactivity than the (Z)-isomer for the former, whereas the (Z)-isomer shows higher reactivity for the latter. (ii) Small negative temperature dependency is observed for the rate constants of the (E)-isomers of CF3CF=CHCl and CHF2CF=CHCl, and slightly larger negative temperature dependency is observed for (Z)-CHF2CF=CHCl than for the (E)-isomers. Our computational results suggest somewhat exaggerated temperature dependency for the (Z)-isomer of CHF2CF=CHCl


Page 20 of 41

Page 21 of 41 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


relative to the experimental data. (iii) In contrast to these three reactants, the temperature dependency of the rate constants for (Z)-CF3CF=CHCl is slightly positive (Figures 1 and S5). The theoretically derived rate constants show weak non-linear behavior in their corresponding Arrhenius plots (Figure S5). The non-linear behavior is mainly caused by the presence of two possible reaction channels for the OH radical to attack CF3CF=CHCl and CHF2CF=CHCl, that is, OH radical attack to the terminal carbon and to the central carbon. Table 3 indicates positive temperature dependency for the rate constants for the attack of the OH radical to the terminal carbon. Meanwhile, the rate constants for the attack of the OH radical to the central carbon show negative temperature dependency except for the reaction of (Z)-CF3CF=CHCl. The latter reaction channels are energetically more preferable and have a larger contribution relative to the former channels. However, the small contribution of the former process results in weak non-linear Arrhenius behavior. Although weak non-linear Arrhenius plots have been reported in recent experimental8,9,23,28 and theoretical17–19 investigations on the OH radical reactions of haloolefins, our experimental measurements in the present study suggest linear relationships for the Arrhenius plots of OH radical reactions of CF3CF=CHCl and CHF2CF=CHCl in the temperature range of 250–430 K.



3.4.3. IR spectra of CF3CF=CHCl and CHF2CF=CHCl The geometries of the (E)- and (Z)-isomers of CF3CF=CHCl and CHF2CF=CHCl were optimized at the M06-2X/aug-cc-pVTZ level of theory. Frequency calculations were then carried out on the optimized geometries at the same level of theory. The calculated vibrational frequencies were scaled according to the procedure prescribed by Laury et al.22 Specifically, frequencies below 1000 cm-1 were scaled using a factor of 0.9698, while higher frequencies were scaled using a factor of 0.9574. The calculated IR absorption cross sections and band strengths are shown in Figure 2 and Table S5, together with the experimentally observed values. As is seen in Figure 2, the calculated wavenumbers of the strong peaks are in satisfactory agreement with the experimental values, with maximum deviations of 30 cm-1. The calculated band strengths fall within the range of 62∼136% of the experimentally determined values.

3.4.4. Atmospherically relevant parameters The lifetime, REs, lifetime-corrected REs, GWPs, and ODPs derived from the theoretically calculated reaction rate constants and IR spectra are listed in Table 2. The calculated lifetimes and ODPs agree with the experimental values within factors of 0.62–2.75. The REs for (E)-CF3CF=CHCl, (Z)-CF3CF=CHCl, (E)-CHF2CF=CHCl, and (Z)-CHF2CF=CHCl were 0.274, 0.231, 0.216, and 0.162 W m-2 ppb-1, respectively. By comparison, the corresponding IF values for these compounds were 0.333, 0.281,


Page 22 of 41

Page 23 of 41 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


0.233, and 0.189 W m-2 ppb-1, respectively. The values of the RE and IF are consistent with the experimental values within a factor of 1.07–1.14 and 1.14–1.32, respectively. The REs and IFs derived from the theoretical calculations were in satisfactory agreement with the experimental values. However, for the lifetime-corrected REs, the agreement between the calculated and observed values decreased by a factor of 0.9– 2.4. The GWP100 estimated using the lifetime-corrected REs developed by Hodnebrog et al.4 were 1.3, 5.4, 0.37, and 0.012 for (E)-CF3CF=CHCl, (Z)-CF3CF=CHCl, (E)-CHF2CF=CHCl, and (Z)-CHF2CF=CHCl, respectively. Relative to experiment, these values are in agreement within a factor of 0.8–6.2. The GWP100 values estimated using the method developed by Pinnock et al.5 are 8.3, 21, 3.7, and 0.4 for (E)-CF3CF=CHCl, (Z)-CF3CF=CHCl, (E)-CHF2CF=CHCl, and (Z)-CHF2CF=CHCl, respectively, and their agreement with the experimental values is within a factor of 0.8–4.0. The extent of agreement between the calculated and observed values for the lifetime-corrected REs and GWPs is worse relative to that for the uncorrected values of RE and IF.



Page 24 of 41

4. Conclusions and Conclusive Remarks The OH radical rate constants and infrared absorption spectra of CF3CF=CHCl and CHF2CF=CHCl isomers have been measured. The atmospheric lifetimes of (E)-CF3CF=CHCl, (Z)-CF3CF=CHCl, (E)-CHF2CF=CHCl, and (Z)-CHF2CF=CHCl following reaction with the OH radical were estimated to be 8.9, 20, 4.6, and 2.6 days, respectively. The global warming potentials for the 100 year time horizon of CF3CF=CHCl and CHF2CF=CHCl isomers are smaller than 1, and the ozone depleting potentials

of

(E)-CF3CF=CHCl,

(Z)-CF3CF=CHCl,

(E)-CHF2CF=CHCl,

and

(Z)-CHF2CF=CHCl are 0.00010, 0.00023, 0.000057, and 0.000030, respectively. Thus, the contribution of these compounds to global warming and stratospheric ozone depletion is expected to be negligible. The hybrid meta DFT (M06-2X) and ab initio (MP2 and CCSD(T)) methods have been applied to calculate the OH radical addition rate constants and IR spectra of the (E)/(Z) isomers of CF3CF=CHCl and CHF2CF=CHCl. The computed OH addition rate constants satisfactorily reproduce the experimentally observed reactivity trends, indicating that the (E)/(Z) reactivity is reversed for CF3CF=CHCl and CHF2CF=CHCl. The calculated IR spectra show reasonable agreement with the experimentally observed ones in terms of both wavenumbers and band strengths of the strong absorption peaks. Atmospherically relevant parameters have also been calculated based on the theoretically derived values. The calculated lifetimes and ODPs agree


Page 25 of 41 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


with the experimental values within a factor of 0.62–2.75. The extent of agreement between the calculated and observed values for lifetime-corrected REs and GWPs is worse relative to that for the uncorrected values of RE and IF. The relationship between the (E)/(Z) energy differences and the (E)/(Z) reactivity differences for the OH radical reactions of CF3CF=CHCl and CHF2CF=CHCl are noteworthy. Our computational results of the (E)/(Z) energy differences are described in Section 3.4.1; the (Z)-isomers of CF3CF=CHCl and CHF2CF=CHCl were found to be lower in energy than the (E)-isomers. High-level ab initio calculations indicated (E)/(Z) enthalpy differences (∆H(298 K)) of 3.8 and 1.6 kcal/mol for CF3CF=CHCl and CHF2CF=CHCl, respectively. Meanwhile, both our experimental measurements and computational results have indicated that the (E)/(Z) reactivity is reversed for CF3CF=CHCl and CHF2CF=CHCl. For CF3CF=CHCl, the higher-energy (E)-isomer is more reactive toward OH radicals than the lower-energy (Z)-isomer. However, the lower-energy (Z)-isomer is more reactive than the higher-energy (E)-isomer for CHF2CF=CHCl. For OH radical reactions of haloolefins, the higher-energy geometrical isomer tends to show a larger rate constant than its lower-energy counterpart.8,26,27 Accordingly, the difference in (E)/(Z) reactivity for CF3CF=CHCl is expected on the basis of its (E)/(Z) energy difference. Meanwhile, the observed difference in (E)/(Z) reactivity for CHF2CF=CHCl is opposite to that expected on the basis of its (E)/(Z) energy difference. Thus, CF3CF=CHCl and CHF2CF=CHCl are



Page 26 of 41

considered to undergo ordinary and anomalous trends in (E)/(Z) reactivity, respectively. The anomalous trend in (E)/(Z) reactivity for olefins substituted with CHF2 groups has also

been

recognized

in

recent

computational

kinetics

investigations

by

Ramanjanryulu and Rajakumar19 on the OH radical reactions of cis- and trans-CHF2CH=CHF. At present, however, we cannot explain clearly the origin of the difference in (E)/(Z) reactivity between CF3CF=CHCl and CHF2CF=CHCl.


Page 27 of 41 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


Supporting Information Tables of experimental conditions and the observed values of the OH radical reaction rate constants of (E)-CF3CF=CHCl, (Z)-CF3CF=CHCl, (E)-CHF2CF=CHCl, and (Z)-CHF2CF=CHCl; integrated infrared absorption band strengths; Infrared cross sectional data between 400 and 2500 cm-1 obtained with spectral resolutions of 1 cm-1; computational procedure for estimating the (E)/(Z) energy differences; calculated values of the (E)/(Z) energy differences; computational procedure for the rate constant calculations; calculated energy differences between the transition states and the reactants; figures of pseudo-first-order decay of OH radical for various (Z)-CF3CF=CHCl concentrations; plot of the observed pseudo-first-order rate constant kobs against (Z)-CF3CF=CHCl concentration; plot of the pseudo-first-order rate constants corrected for background value, kobs - kd against (Z)-CF3CF=CHCl concentration; energy profiles for the rotation of the CF3 and CHF2 groups; comparison of Arrhenius plots of calculated rate constants with experimental values; and the complete author list for reference 11. This material is available free of charge via the Internet at http://pubs.acs.org.

Acknowledgements This work was financially supported by the New Energy and Industrial Technology Development Organization (NEDO). T. U. thanks the Tsukuba Advanced



Computing Center (TACC) for generously providing computational facilities.


Page 28 of 41

Page 29 of 41 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


References (1) Tokuhashi, K.; Takahashi, A.; Kaise, M.; Kondo, S.; Sekiya, A.; Fujimoto, E. Rate Constants for the Reactions of OH Radicals with CF3OCF=CF2 and CF3CF=CF2. Chem. Phys. Lett. 2000, 325, 189–195. (2) Tokuhashi, K.; Chen, L.; Takizawa, K.; Takahashi, A.; Uchimaru, T.; Sugie, M.; Kondo, S.; Sekiya, A. Fluorine Chemistry Research Advances, Chapter 4; Evaluation of the Lifetimes of Fluorinated Compounds: Measurement of Rate Constants for Reactions with OH Radicals, NOVA Science Publishers Inc., New York, 2007: pp.143–241. (3) Prinn, R. G.; Huang, J.; Weiss, R. F.; Cunnold, D. M.; Fraser, P. J.; Simmonds, P. G.; McCulloch, A.; Harth, C.; Salameh, P.; O’Doherty, S.; et al. Evidence for Substantial Variations of Atmospheric Hydroxyl Radicals in the Past Two Decades, Science 2001, 292, 1882–1888. (4) Hodnebrog, Ø.; Etminan, M.; Fuglestvedt, J. S.; Marston, G.; Myhre, G.; Nielsen, C. J.; Shine, K. P.; Wallington, T. J. Global Warming Potentials and Radiative Efficiencies of Halocarbons and Related Compounds: A Comprehensive Review. Rev. Geophys. 2013, 51, 300–378. (5) Pinnock, S.; Hurley, M. D.; Shine, K. P.; Wallington, T. J.; Smyth, T. J. Radiative Forcing of Climate by Hydrochlorofluorocarbons and Hydrofluorocarbons, J. Geophys. Res. 1995, 100 (D11), 23227–23238.



Page 30 of 41

(6) Patten, K. O.; Wuebbles, D. J. Atmospheric Lifetimes and Ozone Depletion Potentials

of

trans-1-Chloro-3,3,3-trifluoropropylene

and

trans-1,2-Dichloroethylene in a Three-Dimensional Model. Atmos. Chem. Phys. 2010, 10, 10867–10874. (7) Sulbaek Andersen, M. P.; Nilsson, E. J. K.; Nielsen, O. J.; Johnson, M. S.; Hurley, M. D.; Wallington, T. J. Atmospheric Chemistry of trans-CF3CH=CHCl: Kinetics of the Gas-Phase Reactions with Cl Atoms, OH Radicals, and O3. J. Photochem. Photobiol. A 2008, 199, 92–97. (8) Gierczak, T.; Baasandorj, M.; Burkholder, J. B. OH + (E)- and (Z)-1-Chloro-3,3,3trifluoropropene-1

(CF3CH=CHCl)

Reaction

Rate

Coefficients:

Stereoisomer-dependent Reactivity. J. Phys. Chem. A 2014, 118, 11015–11025. (9) Orkin, V. L.; Martynova, L. E.; Kurylo, M. J. Photochemical Properties of trans-1-Chloro-3,3,3,-trifluoropropene (trans-CHCl=CHCF3): OH Reaction Rate Constant, UV and IR Absorption Spectra, Global Warming Potential, and Ozone Depletion Potential. J. Phys. Chem. A 2014, 118, 5263–5271. (10) Burkholder, J. B.; Sander, S. P.; Abbatt, J. P. D.; Barker, J. R.; Huie, R. E.; Kolb, C. E.; Kurylo, M. J.; Orkin, V. L.; Wilmouth, D. M.; Wine, P. H. Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies, Evaluation No. 18, JPL Publication

15-10,

Jet

Propulsion

Laboratory,

http://jpldataeval.jpl.nasa.gov.


Pasadena,

2015,

Page 31 of 41 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


(11) Gaussian 09, Revision D.01, Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A. et al., Gaussian, Inc., Wallingford CT, 2009. (12) Zhao, Y.; Truhlar, D. G. Density Functionals with Broad Applicability in Chemistry. Acc. Chem. Res. 2008, 41 (2), 157–167. (13) Zhao, Y.; Truhlar, D. G. The M06 Suite of Density Functionals for Main Group Thermochemistry, Thermochemical Kinetics, Noncovalent Interactions, Excited States, and Transition Elements: Two New Functionals and Systematic Testing of 4 M06-Class Functionals and 12 Other Functionals. Theor. Chem. Acc. 2008, 120 (1-3), 215–241. (14) Dunning, T. H. Gaussian Basis Sets for Use in Correlated Molecular Calculations. I. The Atoms Boron through Neon and Hydrogen. J. Chem. Phys. 1989, 90 (2), 1007–1023. (15) Woon, D. E.; Dunning, T. H. Gaussian Basis Sets for Use in Correlated Molecular Calculations. III. The Atoms Aluminum through Argon. J. Chem. Phys. 1993, 98 (2), 1358–1371. (16) Uneyama, K. Organofluorine Chemistry; Blackwell Publishing Ltd: Oxford, U.K., 2006. (17) Balaganesh, M., Rajakumar, B. Rate Coefficients and Reaction Mechanism for the Reaction of OH Radicals with (E)-CF3CH=CHF, (Z)-CF3CH=CHF,



Page 32 of 41

(E)-CF3CF=CHF, and (Z)-CF3CF=CHF between 200 and 400 K: Hybrid Density Functional Theory and Canonical Variational Transition

State

Theory

Calculations. J. Phys. Chem. A 2012, 116, 9832–9842. (18) Balaganesh, M.; Rajakumar, B. Mechanism, Kinetics and Atmospheric Fate of CF3CH=CH2, CF3CF=CH2, and CF3CF=CF2 by Its Reaction with OH-Radicals: CVT/SCT/ISPE and Hybrid Meta-DFT Methods. J. Mol. Graph. Model. 2014, 48, 60–69. (19) Ramanjaneyulu, C.; Rajakumar, B. Kinetic Parameters for the Reaction of OH Radical with cis-CHF=CHCHF2, trans-CHF=CHCHF2, CF2=CHCHF2 and CF2=C=CHF: Hybrid Meta DFT and CVT/SCT/ISPE Calculations. J. Fluorine Chem. 2015, 178, 266–278. (20) Zhang, W.; Du, B. Quantum Chemical Study of the Mechanism for OH-Initiated Atmospheric Oxidation Reaction of (Z)-CF3CF=CHF. Comput. Theor. Chem. 2012, 991, 22–31. (21) Pople, J. A.; Head-Gordon, M.; Raghavachari, K. Quadratic Configuration Interaction. A General Technique for Determining Electron Correlation Energies. J. Chem. Phys. 1987, 87 (10), 5968–5975. (22) Laury, M. L.; Boesch, S. E.; Haken, I.; Sinha, P.; Wheeler, R. A.; Wilson, A. K. Harmonic Vibrational Frequencies: Scale Factors for Pure, Hybrid, Hybrid Meta, and Double-Hybrid Functionals in Conjunction with Correlation Consistent Basis


Page 33 of 41 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


Sets. J. Comput. Chem. 2011, 32 (11), 2339–2347. (23) Baasandorj, M.; Ravishankara, A. R.; Burkholder, J. B. Atmospheric Chemistry of (Z)-CF3CH=CFCF3: OH Radical Reaction Rate Coefficient and Global Warming Potential J. Phys. Chem. A 2011, 115, 10539–10549. (24) Wallington, T.J.; Sulbaek Andersen, M. P.; Nielsen, O. J. Atmospheric Chemistry of Short-Chain Haloolefins: Photochemical Ozone Creation Potentials (POCPs), Global Warming Potentials (GWPs), and Ozone Depletion Potentials (ODPs), Chemosphere 2015, 129, 135–141. (25) Tokuashi, K.; Nagai, H.; Takahashi, A.; Kaise, M.; Kondo, S.; Sekiya, A.; Takahashi, M.; Gotoh, Y.; Suga, A. Measurement of the OH Reaction Rate Constants for CF3CH2OH, CF3CF2CH2OH, and CF3CH(OH)CF3. J. Chem. Phys. 1999, 103, 2664–2672. (26) Hurley, M. D.; Ball, J. C.; Wallington, T. J. Atmospheric Chemistry of the Z and E Isomers of CF3CF=CHF; Kinetics, Mechanisms, and Products of Gas-Phase Reactions with Cl Atoms, OH Radicals, and O3 J. Phys. Chem. A 2007, 111, 9789–9795. (27) Anderson, L. L.; Østerstrøm, F. F.; Andersen, M. P. S.; Nielsen, O, J.; Wallington, T. J. Atmospheric Chemistry of cis-CF3CH=CHCl (HCFO-1233zd(Z)): Kinetics of the Gas-Phase Reactions with Cl Atoms, OH Radicals, and O3. Chem. Phys. Lett. 2015, 639, 289–293.



(28) Papadimitriou, V. C.; Talukdar, R.; Portmann, R. W. Ravishankara, A. R.; Burkholder, J. B. CF3CF=CH2 and (Z)-CF3CF=CHF: Temperature Dependent OH Rate Coefficients and Global Warming Potentials Phys. Chem. Chem. Phys. 2008, 10, 808–820.


Page 34 of 41

Page 35 of 41 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 Captions

Figure 1 Arrhenius plot for the reactions of OH with CF3CF=CHCl and CHF2CF=CHCl isomers. The solid lines represent least squares fit to our data. The error bars are at the 95% confidence level and do not include systematic errors.

Figure 2 IR absorption cross sections of CF3CF=CHCl and CHF2CF=CHCl isomers in 760 Torr of N2 measured using FTIR at 1 cm-1 resolution. Thin lines represent radiative forcings reported by Hodnebrog et al.4 at 1 cm-1 resolution. Broken lines represent calculated cross sections. Digitized spectra are available in the Supporting Information.



Table 1

Page 36 of 41

Arrhenius Parameters for Reactions of OH with CF3CF=CHCl and CHF2CF=CHCl Isomers.a

sample (E)- CF3CF=CHCl (Z)- CF3CF=CHCl (E)- CHF2CF=CHCl (Z)- CHF2CF=CHCl

A × 1012, cm3 molecule-1 s-1

E/R, K

k298 × 1012, cm3 molecule-1 s-1

1.09±0.03 0.802±0.019 1.50±0.03 1.36±0.03

-50±10 100±10 -160±10 -360±10

1.30±0.01 0.584±0.003 2.54±0.01 4.48±0.02

a

The quoted errors represent 95% confidence level from non-linear least squares analysis and do not include systematic errors.


Page 37 of 41 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


Table 2

Atmospheric Lifetimes, Radiative Efficiencies (RE), GWPs, and ODPs of CF3CF=CHCl and CHF2CF=CHCl Isomers. experimental a

sample

(E)-CF3CF=CHCl (Z)-CF3CF=CHCl (E)-CHF2CF=CHCl (Z)-CHF2CF=CHCl

lifetime, days 8.9 20 4.6 2.6

RE, W m-2 ppb-1 0.241 0.216 0.195 0.148

RE (lifetime corr.),b W m-2 ppb-1 0.023 0.039 0.010 0.0046

calculated a

GWP100

ODP

lifetime, days

0.23 0.88 0.060 0.016

0.00010 0.00023 0.000057 0.000030

21 55 11 2.1

a

RE: Radiative efficiency integrated between 470–2000 cm-1. b RE (lifetime corr.): Lifetime-corrected radiative efficiency.

37

ACS Paragon Plus Environment

RE, W m-2 ppb-1 0.274 0.231 0.216 0.162

RE (lifetime ODP corr.),b GWP100 -2 -1 W m ppb 0.052 1.3 0.00021 0.086 5.4 0.00065 0.025 0.37 0.00013 0.0043 0.012 0.000019


Table 3

Page 38 of 41

Calculated and Experimentally Determined Rate Constants of the Reactions of the (E)- and (Z)-isomers of CF3CF=CHCl and CHF2CF=CHCl with OH Radical.a

T, K

250 273 298 331 375 430

kterminal × 1012 0.0504 0.0567 0.0637 0.0742 0.0891 0.1101

250 273 298 331 375 430

0.0231 0.0277 0.0332 0.0410 0.0527 0.0692

250 273 298 331 375 430

0.119 0.130 0.143 0.161 0.186 0.228

250 273 298 331 375 430

0.810 0.801 0.802 0.818 0.853 0.922

calculated b kcentral × 1012

ktotal × 1012

(E)-CF3CF=CHCl 0.657 0.707 0.559 0.616 0.485 0.548 0.429 0.503 0.384 0.473 0.360 0.470 (Z)-CF3CF=CHCl 0.180 0.203 0.178 0.206 0.179 0.212 0.183 0.224 0.193 0.246 0.210 0.279 (E)-CHF2CF=CHCl 1.135 1.25 0.989 1.12 0.886 1.03 0.800 0.960 0.736 0.922 0.703 0.931 (Z)-CHF2CF=CHCl 11.90 12.0 7.86 7.94 5.45 5.53 3.74 3.82 2.56 2.65 1.85 1.94

a

experimental c kOH × 1012 1.35±0.01 1.32±0.01 1.30±0.01 1.28±0.01 1.26±0.01 1.23±0.01 0.549±0.004 0.567±0.003 0.584±0.003 0.602±0.003 0.623±0.004 0.644±0.005 2.81±0.02 2.66±0.01 2.54±0.01 2.41±0.01 2.28±0.01 2.16±0.02 5.64±0.04 5.00±0.03 4.48±0.02 3.98±0.02 3.51±0.02 3.11±0.02

Rate constants are given in units of cm3 molecule-1 s-1. b Only OH radical addition pathways are considered for computing the rate constants. c Derived from Arrhenius rate parameters.


Page 39 of 41 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 1



Figure 2


Page 40 of 41

Page 41 of 41 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


TOC Graphic


(Z

Recommend Documents