Rate Constants for the Reactions of OH Radicals with Fluorinated

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A: Kinetics and Dynamics

Rate Constants for the Reactions of OH Radicals with Fluorinated Ethenes: Kinetic Measurements and Correlation between Structure and Reactivity Kazuaki Tokuhashi, Kenji Takizawa, and Shigeo Kondo J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.7b11653 • Publication Date (Web): 23 Apr 2018 Downloaded from http://pubs.acs.org on April 23, 2018

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The Journal of Physical Chemistry

Rate Constants for the Reactions of OH Radicals with Fluorinated Ethenes: Kinetic Measurements and Correlation between Structure and Reactivity

Kazuaki Tokuhashi, 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 (e-mail: [email protected], Phone: +81-29-861-9441)

Short Title: Rate constant for OH with Fluorinated Ethenes

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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

Abstract The rate constants for the reaction of OH radicals with four fluorinated ethenes (CF2=CHF, (E)-CHF=CHF, CF2=CH2, and CHF=CH2) have been measured over the temperature range of 250–430 K. Kinetic measurements have been carried out using flash photolysis and laser photolysis methods combined with a laser-induced fluorescence technique. The Arrhenius expressions for the rate constant have been determined as k(CF2=CHF) = (3.12 ± 0.11) × 10−12·exp[(270 ± 10) / T], k((E)-CHF=CHF) = (3.75 ± 0.08) × 10−12·exp[(230 ± 10) / T], k(CF2=CH2) = (1.15 ± 0.07) × 10−12·exp[(230 ± 20) / T], and k(CHF=CH2) = (1.16 ± 0.09) × 10−12·exp[(390 ± 20) / T] cm3 molecule−1 s−1. Infrared absorption spectra of the fluorinated ethenes have been measured at room temperature. The atmospheric lifetimes and global warming potentials of the fluorinated ethenes have been estimated. The correlation between the reactivity and the structure of the halogenated ethenes has been investigated by considering the structure containing the atoms attached to the carbons on both sides of the double bond. The calculated rate constants of 14 halogenated ethenes showed agreement with the measured rate constants within a factor of 2, except for that of one compound.


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1. Introduction Halogenated alkenes have been developed as alternatives to chlorofluorocarbons, hydrochlorofluorocarbons, and hydrofluorocarbons, owing to their very short atmospheric lifetimes. For example, CF2=CH2 has recently been approved by the standards committee of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)

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as a new refrigerant and is expected to be

used as a component of blended refrigerants suitable for use as alternatives to CHF3 in very-low-temperature refrigeration systems. CF2=CHF has been developed as a candidate for low-temperature refrigerants. (E)-CHF-CHF has also been considered as a candidate for refrigerant R-410A, which is a blended refrigerant of CH2F2 (50 wt%) and CF3CHF2 (50 wt%) 2. However, halogenated alkenes may contribute to global warming when released into the atmosphere, because they have absorption originated from the C-F bond in the infrared region of the atmospheric window 3. Prior to their large-scale use, an assessment of the environmental impacts of these compounds is necessary. The global warming potential (GWP) depends on the removal rate in the atmosphere and the infrared absorption intensities. Because the main decomposition pathway of the halogenated alkenes is the addition of OH radicals to the double bond, the atmospheric lifetime can be estimated from the reaction rate constant with OH radicals. Therefore, it is indispensable to evaluate the reaction rate constant with OH radicals and the infrared spectra.



In previous studies related to the environmental impacts of fluorinated ethenes, the temperature dependencies of the reaction rate constants of CF2=CHF with OH radicals have been reported by two groups using the absolute 4 and the relative rate 5 methods, and the IR absorption spectra have been reported by Baasandorj and Burkholder 4. For CF2=CH2, Howard

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reported the reaction rate constant at room

temperature using the absolute rate method, and the temperature dependencies of the reaction rate constants have been reported by two groups using the absolute 7 and the relative rate 5 methods. Its IR absorption spectra have been reported by Baasandorj et al. 7. For CHF=CH2, the temperature dependencies of the reaction rate constants have been reported by two groups using the absolute rate method 7, 8 and by Chen et al. using the relative rate method 5. Its IR absorption spectra have been reported by two groups 7, 9. There have been no reports on the reaction rate constants and IR absorption spectra of (E)-CHF=CHF. Apart from the experimental measurements of the reaction rate constants of halogenated alkenes, the development of an estimation method of the reactivity of halogenated alkenes seems to be useful. However, the effect of the substitution of H with F on the reactivity of an alkene is complicated. For example, the change in the reaction rate constant with OH radicals (in units of 10−12 cm3 molecule−1 s−1) by fluorination on the simplest alkene, ethene is as follows: CH2=CH2 (8.50) > CHF=CH2 (4.33) > CF2=CH2 (2.44) < CF2=CHF (7.73) < CF2=CF2 (10.0). Orkin et al. 10

suggested that the change in reactivity by fluorination depends mainly on the


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geometrical localization of the π-electron density. However, the quantitative change in reactivity has not yet been clarified. In addition to fluorinated alkenes, hydrochlorofluoroalkenes such as (E)-CF3CH=CHCl have recently been gaining attention as new alternatives

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. Accordingly, the understanding of the change in

reactivity by substitution with Cl also seems to be useful. The effect of substitution of H with Cl on the reactivity of ethene is quite different from that with F. The change in the reaction rate constant with OH radicals by the substitution with Cl is as follows: CH2=CH2 (8.50) > CHCl=CH2 (6.90) < CCl2=CH2 (10.5) >> CCl2=CHCl (2.20) >> CCl2=CCl2 (0.170). The change in reactivity by Cl substitution has not been understood quantitatively. In order to develop an estimation method of the reactivity of halogenated alkenes, it is indispensable to investigate the correlation between the reactivity and the structure of the compound. In this study, we first report on the results of the kinetic measurements of the reaction of OH radicals with four fluorinated ethenes, CF2=CHF, (E)-CHF=CHF, CF2=CH2, and CHF=CH2, over the temperature range of 250–430 K. Infrared absorption spectra of these compounds have been measured, and the atmospheric lifetimes with respect to the reaction with OH radicals, as well as the GWP have been estimated. The kinetic measurement of various compounds using the same technique is expected to improve the reliability of the measured rate constants for individual compounds. Second, we examine the change in the reactivity of halogenated ethenes



by the substitution with F and Cl. Furthermore, the correlation between the reactivity and the structure of the compound has been calculated by considering the structure containing the atoms attached to the carbons on both sides of the double bond.


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2. Experimental The OH reaction rate constants have been measured for fluorinated ethenes over the temperature range of 250–430K by using the absolute rate method. The experimental apparatus and procedure for the kinetic measurements have been described in detail elsewhere 12, 13. Briefly, the kinetic measurements have been carried out under pseudo-first-order reaction conditions of a large excess of the sample (fluorinated ethenes) concentration with respect to the initial concentration of OH radicals during the measurements. OH radicals have been generated either by the flash photolysis (FP) or laser photolysis (LP) methods. The change in concentration of OH radicals by the reaction was monitored by means of the laser-induced fluorescence (LIF) method. In the case of the FP method, water vapor was directly photolyzed with pulsed light from a Xe flash lamp (EG & G, FX-193U, 600–1300 V, 2 µF, pulse energy: 0.36– 1.69 J pulse−1, typically 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. The photolyzing light is weakly focused by two quartz lenses, and irradiated to the reaction cell along the axial line through the quartz window. The experimental apparatus used in the LP method was almost the same as that in the FP method, except for the light source used to produce OH radicals and the gas supplied to the reactor. In the case of the LP method, the following three OH sources



have been examined. First, OH radicals were produced by the reaction, O(1D) + H2O → 2OH (LP-H2O method), where O(1D) atoms are generated by the photodissociation of N2O with an ArF excimer laser (Japan Storage Battery, EXL-210 or Coherent, ExciStar XS) of wavelength 193 nm. The initial concentrations of N2O and H2O for the LP-H2O method were (0.4–8.2) × 1014 and (3.4–8.7) × 1015 molecule cm−3, respectively. Second, the reaction of O(1D) + CH4 → OH + CH3 was used as a water-free OH production method (LP-CH4 method). The initial concentrations of N2O and CH4 for the LP-CH4 method were (1.4–8.5) × 1014 and (1.4–4.8) × 1016 molecule cm−3, respectively. Third, the direct photolysis of H2O2 by using a KrF excimer laser (Japan Storage Battery, EXL-210) was also examined (LP-H2O2 method). He (helium) was used as a carrier gas for the LP-H2O, LP-CH4, and LP-H2O2 methods. The power density of the excimer laser at the exit window of the reactor was 2–5 mJ cm−2 pulse−1. The optical path region between the flash lamp (or excimer laser for the LP method) and reaction cell was purged with dry N2. He (99.995%), Ar (99.995%), and CH4 (99.9%) were used without further purification. N2O (99.999%) was purchased as a mixture with He, with a N2O concentration of approximately 1%. The reduction in concentration of OH radicals by the reactions was measured by the LIF technique. The excitation light was from a frequency-doubled tunable dye laser (Quantel, TDL90), and the wavelength was tuned to approximately 308 nm. The dye laser was pumped by pulsed light from a frequency-doubled Nd:YAG laser (532


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nm). The repetition rate of the YAG laser and photolysis light (flash lamp or excimer laser) was set at 10 Hz. Fluorescence signals due to OH radicals whose wavelength was approximately 308 nm and slightly shorter than the excitation light were monitored perpendicularly to both the photolysis light and the excitation light of the LIF method. The scattered light due to the excitation light and photolysis light was reduced by a monochromator (Jarrell-Ash, Monospec 25). A photomultiplier tube was used to monitor the fluorescence signal from the OH radicals. The signals were amplified and accumulated by a multichannel scaler/averager (Stanford Research Systems, SR430), and stored in a microcomputer for further data processing. The flow rate of fluorinated ethenes and various gases were measured and controlled by calibrated mass flow controllers. H2O or H2O2 vapor was supplied by bubbling a certain part of carrier gas through a vessel filled with H2O or H2O2 at room temperature. The total gas pressure in the reactor was measured by using a capacitance manometer, and was kept constant by an electrically controlled exhaust throttle valve located downstream of the reactor. In order to prevent the accumulation of photofragments or reaction products in the reactor, all experiments were carried out under slow flow conditions (the linear flow velocity of the gas mixture ranged between approximately 40–150 cm s−1). The temperature of the reactor was maintained either by an electric heater (331– 430 K), or by circulating water (298–331 K) or coolant (Fluorinert, 250–273 K) in the



outer jacket of the reactor from a temperature-controlled bath. It was measured by a thermocouple at a location approximately 1–2 cm downstream from the probe laser beam. During the experiments, the variation in temperature across the viewing zone was maintained within ±2 K over the temperature range examined. In order to ensure that the experimental data were free from any systematic errors, the experiments were repeated at intervals from several days to several months under a variety of flow conditions (total pressure range of 5–200 Torr; residence time range of 0.1–0.4 s). The purity of fluorinated ethenes was determined by using a gas chromatograph with an FID detector (Shimadzu, GC-2014 and GC-14B), and the integrated intensity of the main peak relative to the total area was taken as the sample purity. The analysis was carried out using various columns. The lowest value obtained using various columns was taken as the purity of the sample. The sample of CF2=CHF purchased from SynQuest contains a small amount of stabilizer, whereas the sample of CF2=CHF obtained from Asahi Glass does not contain stabilizer. The measurements of the OH reaction rate constant and Fourier transform infrared (FTIR) spectroscopy and gas chromatography (GC) analyses were carried out using both samples. As a result, no detectable differences between these two samples were found. The samples of (E)-CHF=CHF, CF2=CH2, and CHF=CH2 do not contain stabilizers. The sample purities of CF2=CHF (Asahi Glass and SynQuest), (E)-CHF=CHF (Asahi Glass), CF2=CH2 (SynQuest), and CHF=CH2 (SynQuest) were found to be 99.6, 99.96, 99.93,


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and 99.99%, respectively, which are sufficiently high that the samples were used for the measurements without further purification. The infrared spectra were measured with a FTIR (Shimadzu FTIR-8700) equipped with a Pyrex glass cell (10 cm optical path length) with KBr windows. A total of 50 scans were used to obtain both the sample and background spectra between 400 and 4000 cm−1 at a spectral resolution of 1 cm−1. The sample gas was introduced into the evacuated IR cell at an appropriate pressure. Then, dry N2 was added to the IR cell until the total pressure became 760 Torr. The background spectrum was measured with the IR cell filled with dry N2 at approximately 760 Torr. For each sample, 10 spectra with different sample partial pressures were measured, and the infrared absorption cross-sections were obtained from each spectrum. Because the FTIR tends to show significantly large absorption peaks due to H2O and CO2 in the ambient air, the optical path of the FTIR was purged by dry N2 to decrease the absorption due to ambient H2O and CO2, to the extent that the influence of their absorption did not appear after subtracting the background spectrum. Contrary to CO2, it is more difficult to remove H2O. In order to prevent H2O vapor from permeating the FTIR equipment, dry air was allowed to flow continuously in the region between the optical part and outer case of the FTIR spectrometer.



3. Results and Discussion 3.1. OH Reaction Rate Constant The reaction rate constants for OH with fluorinated ethenes were measured over the temperature range of 250–430 K. The OH rate constants measured in the present study and the pressure range are summarized in Table 1. Here, the error limits of our results are at the 95% confidence level derived from a linear least-squares fit to the plot of the first-order rate constant versus reactant concentration, and the systematic errors are not considered. The systematic errors in our experiments are estimated to be less than ±10%. Detailed information about the experimental conditions is shown in the Supporting Information (Tables S1–S4). The reaction rate constants were found to be independent of pressure and residence time in the range shown in Table 1, within the experimental errors. Examples of an OH decay plot, and a plot of the observed pseudo-first-order decay rate versus CF2=CHF concentration are shown in the Supporting Information (Figure S1). Because the plot of ln[OH] versus reaction time for various CF2=CHF concentrations (0–1.58 × 1015 molecule cm−3) in Figure S1 shows a slightly scattered linear relationship, the pseudo-first-order decay rate (kobs) can be derived from the slopes of the straight lines by a least-squares fit to each decay plot. The inset of Figure S1 shows a plot of the pseudo-first-order decay rate versus CF2=CHF concentration. The plot shows a slightly scattered linear relationship. The rate constant for the reaction of OH with CF2=CHF can be derived from the slope of


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the straight line by a linear least-squares fit to the observed data. The intercept of the plot of kobs versus reactant concentration for zero reactant (k0) is attributed to the diffusion of OH radicals from the viewing zone and reaction of OH with H2O2 for the LP-H2O2 method, and is partially caused by the reaction of OH with impurities contained in the gas mixture. It was dependent on the experimental conditions, i.e., total pressure, concentration of each component apart from the sample, and so on. For each set of the plot of kobs versus reactant concentration for various experimental conditions, the value of k0 was subtracted from kobs. Figure S2 in the Supporting Information shows the pseudo-first-order decay rate corrected for the background value (kobs − k0) versus CF2=CHF concentration for various temperatures. The plots show linear relationships. The rate constants for the reaction of OH with CF2=CHF for each temperature can be derived from the slope of the straight line by a linear least-squares fit to the observed data. In all cases, the OH decay showed an exponential decay, and the linearity and the scatter of the plotted points for individual experiments were highly similar to those shown in Figure S1. The linearity and the scatter of kobs − k0 versus reactant concentration for various temperatures, methods, and samples were similar to those shown in Figure S2. An Arrhenius plot of the rate constants is shown in Figure 1. As can be seen from Figure 1, the plots show Arrhenius behavior within the experimental errors over the temperature range examined. The differences among the results obtained by the



different methods were small. Thus, it is concluded that the systematic errors among the individual experimental techniques as well as the unexpected fluctuation of experimental conditions are negligible. The Arrhenius plots show a negative temperature dependence. Table 2 lists the Arrhenius parameters and the rate constants at 298 K derived from the Arrhenius parameters. The literature data for OH with fluorinated ethenes are also listed in Table 2 and plotted in Figure 1. Howard

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has measured the OH rate constant of CF2=CH2 at 296 K by using the

discharge flow and laser magnetic resonance methods. Perry et al. 8 have measured the OH rate constant of CHF=CH2 over the temperature range of 299–426 K by using the FP and resonance fluorescence methods. Chen et al.

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have measured the OH rate

constants of CF2=CHF, CF2=CH2, and CHF=CH2 over the temperature range of 253– 328 K by using the relative rate method. Baasandorj et al. 7 have measured the OH rate constants of CF2=CH2 and CHF=CH2 over the temperature range of 212–373 K by using a combination of the LP and LIF methods. Using the same technique, Baasandorj and Burkholder

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have recently measured the OH rate constants of

CF2=CHF over the temperature range of 212–373 K. There are no other reported values of the rate constants for OH with (E)-CHF=CHF. The uncertainties reported by Chen et al. 5 listed in Table 2 have a precision of two standard deviations. They reported that the uncertainties in the GC analysis (less than 2%) and in the rate constants of reference compounds (20–25%) could add an


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additional systematic uncertainty to the uncertainties of the rate constants. The rate constants of OH with CF2=CHF, CF2=CH2, and CHF=CH2 reported by Chen et al. 5 are approximately 2–16% larger than those of our results at 298 K, and agree with ours within 20% over the entire temperature range. Thus, by considering systematic errors, both results overlap within their estimated uncertainty ranges. The error limits of the rate constants at 296 K reported by Baasandorj and co-workers

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are the 2σ

uncertainties, and include the estimated systematic errors. At 296 K, the rate constants of OH with CF2=CHF, CF2=CH2, and CHF=CH2 reported by Baasandorj and co-workers 4, 7 are approximately 13–20% larger than ours. However, if our systematic errors (less than 10%) are taken into account, both results overlap within the estimated uncertainty ranges. Howard

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reported that the accuracy of their measurements is

estimated to be approximately ±20%. The room temperature rate constant of OH with CF2=CH2 reported by Howard 6 is 20% smaller than ours, but the two results overlap when the estimated uncertainties are considered. The error limits reported by Perry et al.

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are the estimated overall error limits. At 299 K, their rate constant of OH with

CHF=CH2 is approximately 28% larger than ours, and even if the estimated uncertainties are taken into account, the two results are not identical. The reason for this discrepancy is not known. Baasandorj and co-workers 4, 7 observed OH regeneration in the reactions of OH with CF2=CHF, CF2=CH2, and CHF=CH2 at long reaction times. Because we



measured the rate constants of OH with CF2=CHF, CF2=CH2, and CHF=CH2 at reaction times shorter than 0.25, 0.4, and 0.3 m-s, respectively, and did not measure at long reaction times, a curvature in the OH decay due to OH regeneration was not clearly observed.

3.2. IR Absorption Spectra The infrared absorption spectra of the four fluorinated ethenes mixed with N2 in the range of 400–2500 cm−1 at room temperature are shown in Figure 2. The total pressure of the sample-N2 mixture is 760 Torr. The infrared spectra of CF2=CHF, (E)-CHF=CHF, CF2=CH2, and CHF=CH2 measured over the partial pressure range of 1.0–4.8, 2.1–7.1, 1.0–4.0, and 2.3–12.7 Torr, respectively, obeyed the Beer–Lambert law. The infrared absorption band strengths for the fluorinated ethenes and the digitized infrared spectra are available in the Supporting Information (Tables S5 and S7). Here, the error limits of our results are the 95% confidence level from the integrated absorption cross-section of individual spectra with different concentrations and the systematic errors are not considered. The systematic errors in our IR measurements associated with the optical path length (1%) and pressure (2.5–3%) and temperature (0.7–1%) measurements were estimated to be less than 3%. Baasandorj et al. 7 reported that the uncertainty in their experiment was less than approximately 2%, and Stoppa et al.9 reported that their uncertainty was less than approximately 6%.


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Baasandorj et al.

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reported the absorption band strengths of CF2=CH2 as 8.94 ±

0.15 (745–860 cm−1), 15.24 ± 0.08 (870–1010 cm−1), 37.62 ± 0.14 (1180–1440 cm−1), 3.57 ± 0.03 (1560–1660 cm−1), and 39.28 ± 0.17 (1650–1820 cm−1), in units of 10−18 cm2 molecule−1 cm−1. The absorption band strengths of our experiment were 9.02 ± 0.24, 14.80 ± 0.19, 36.02 ± 0.18, 3.50 ± 0.04, and 37.87 ± 0.22 for the corresponding integration range, which agree with their values within the estimated uncertainties. They also reported the absorption band strengths of CHF=CH2 as 18.5 ± 0.16 (770– 1050 cm−1), 14.6 ± 0.11 (1050–1250 cm−1), and 14.9 ± 0.15 (1500–1740 cm−1), in units of 10−18 cm2 molecule−1 cm−1. We obtained the absorption band strengths as 18.76 ± 0.23, 14.65 ± 0.12, and 15.44 ± 0.09, for the same integration range, which agree with their values within 3.5%. The absorption band strengths of CHF=CH2 reported by Stoppa et al.9, 18.33 ± 0.11 (610–1050 cm−1), 12.93 ± 0.12 (1050–1250 cm−1), and 13.9 ± 0.2 (1520–1720 cm−1), in units of 10−18 cm2 molecule−1 cm−1, are 5.5–11.7% smaller than our values (19.39 ± 0.29, 14.65 ± 0.12, and 15.41 ± 0.08, for the same integration range). For the band strength of 610–1050 cm−1, the present results and those of Stoppa et al.9 overlap within the estimated uncertainties. However, the band strengths of the other regions are 10–12% smaller than the present results, and even if the estimated uncertainties are taken into consideration, the two results seem not to be identical. For CF2=CHF, Baasandorj and Burkholder

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have recently

reported the absorption band strengths as 5.12 ± 0.05 (700–800 cm−1), 10.1 ± 0.04



(870–980 cm−1), 25.4 ± 0.09 (1060–1210 cm−1), 55.7 ± 0.14 (1210–1440 cm−1), 1.78 ± 0.05 (1455–1535 cm−1), and 12.5 ± 0.03 (1700–1910 cm−1), in units of 10−18 cm2 molecule−1 cm−1. The absorption band strengths of our experiment were 4.70 ± 0.04, 8.88 ± 0.06, 22.28 ± 0.14, 47.85 ± 0.21, 1.49 ± 0.08, and 10.85 ± 0.10 for the corresponding integration range. The results by Baasandorj and Burkholder are approximately 9–19% greater than the present results and the two results seem not to be identical, even if the estimated uncertainties are considered. Whereas the absorption band strengths of CF2=CH2 and CHF=CH2 reported by Baasandorj et al. 7 agree with our values within the estimated uncertainties, those of CF2=CHF reported by Baasandorj and Burkholder

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do not agree with our values. The purity of CF2=CHF

used in the present study (99.6%) is slightly better than that used by Baasandorj and Burkholder 4 (98%). As mentioned in the Experimental section, the stabilizer contained in CF2=CHF did not influence the results of the IR measurements. Thus, neither the difference in apparatus, the sample purity, nor the stabilizer seems to cause the difference in the absorption band strengths of CF2=CHF between the present results and those of Baasandorj and Burkholder. 4 The reason for these discrepancies is not clear. There are no other reported IR absorption spectra for (E)-CHF=CHF.

3.3 Atmospheric Implications Using the rate constants measured in this study, the atmospheric lifetimes of the


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fluorinated ethenes with respect to the reaction with OH radicals are estimated from an OH concentration of 1 × 106 molecules cm−3 (Prinn et al. 14, Montzka et al. 15) and the reaction rate constant at 298 K derived from the Arrhenius parameters listed in Table 2. The estimated lifetimes of the fluorinated ethenes are listed in Table 3. The GWP is the integrated radiative forcing (RF) over a time horizon following the pulsed emission compared to RF of a reference gas (usually, CO2, in units of kg), and is calculated from the absolute GWP (AGWP) of a compound relative to the AGWP of CO2. Here, the AGWP of a compound is calculated from the radiative efficiencies (RE), lifetime, and time horizon, and the AGWP of CO2 is 9.171 × 10−14 W m2 year (kg CO2)−1 for a time horizon of 100 years (Hodnebrog et al.

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). The RE

for the fluorinated ethenes were estimated using the infrared absorption spectra measured in this work and the estimation method reported by Hodnebrog et al. 16. The RE for CF2=CHF, (E)-CHF=CHF, CF2=CH2, and CHF=CH2 were calculated to be 0.092, 0.084, 0.084, and 0.078 W m−2 ppb−1, respectively, using a 1-cm−1 resolution model. The instantaneous forcings (IF) were calculated to be 0.097, 0.089, 0.086, and 0.083 W m−2 ppb−1, respectively, using 10 cm−1 resolution reported by Pinnock et al. 17. Baasandorj et al. 7 reported the IF for CF2=CH2 and CHF=CH2 as 0.086 and 0.084 W m−2 ppb−1, respectively, using the method reported by Pinnock et al.

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The IF of

CF2=CH2 and CHF=CH2 estimated in this work agree with the values reported by Baasandorj et al. 7.



Hodnebrog et al.

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presented a method for estimating the radiative efficiency of

very short-lived compounds from the RE obtained using the well-mixed gas approach based on the lifetime correction. The lifetime-corrected RE are listed in Table 3, and were decreased 0.020, 0.019, 0.054, and 0.032 times for CF2=CHF, (E)-CHF=CHF, CF2=CH2, and CHF=CH2, respectively, from the well-mixed ones. The GWPs for the 100-year time horizon (GWP100) of the fluorinated ethenes using lifetime-corrected RE are listed in Table 3. The GWP100 values of the fluorinated ethenes estimated in this study are smaller than 1, and the influence on climate change of these compounds seems to be small. However, the GWP100 calculated using the approximation method developed by Pinnock et al. 17 are 0.3, 0.3, 1.1, and 0.8 for CF2=CHF, (E)-CHF=CHF, CF2=CH2, and CHF=CH2, respectively. Baasandorj et al.

7

reported the GWP100 of

CF2=CH2 and CHF=CH2 as 0.9 and 0.7, which agree with the present results. Recently, Baasandorj and Burkholder

4

reported RE and lifetime-corrected RE of CF2=CHF as

0.109 and 0.00153 W m−12 ppb−1, respectively, using the well-mixed gas approach reported by Hodnebrog et al.

16

. Using the lifetime-corrected RE, they reported

GWP100 as 0.00392. The GWP100 reported by Baasandorj and Burkholder

4

is

approximately 0.73 times the present result. The disagreement between the two results seems to be due to the difference in the lifetime and lifetime-corrected RE of CF2=CHF.


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3.4 Substitution Effects on Reactivity Table S6 shows the ratio of the room temperature rate constants of OH radicals with CXY=CZW against CXY=CH2 (X, Y, Z, W =H, F, Cl). As is apparent from Table S6, if the CH2 group of CH2=CH2, CF2=CH2, CCl2=CH2, and CHF=CH2 is substituted for the CF2 group, the reactivities of CH2=CH2 and CCl2=CH2 are reduced by factors of 0.29 and 0.71, whereas the reactivities of CF2=CH2 and CHF=CH2 increase by factors of 4.10 and 1.79, respectively. Similarly, if the CH2 group of CH2=CH2, CF2=CH2, CCl2=CH2, CHF=CH2, and CHCl=CH2 is substituted for a CXY (X, Y= H, F, Cl) group, the change in the reactivity is dependent on the atoms attached to the carbon on the opposite side of the double bond. Thus, in order to explain the reactivity of halogenated ethenes, it is necessary to consider not only the substituent group but also the influence of the atom attached to the carbon on the opposite side of the double bond. In order to examine whether it is possible to explain the reactivity by considering the structure containing the atoms attached to the carbons on both sides of the double bond, we calculated the rate constant by the following equation. kcal = k(>C=CC=CC=CC=CC=C

Rate Constants for the Reactions of OH Radicals with Fluorinated

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