(Z

Article Cite This: J. Phys. Chem. A 2019, 123, 4834−4843

pubs.acs.org/JPCA

Rate Constants for the Reactions of OH Radicals with the (E)/(Z) Isomers of CFCl=CFCl and (E)‑CHF=CHF Kazuaki Tokuhashi, Tadafumi Uchimaru, Kenji Takizawa,* and Shigeo Kondo National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba Ibaraki 305-8565, Japan

Downloaded via UNIV OF SOUTHERN INDIANA on July 21, 2019 at 18:33:05 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: The rate constants for the OH radical reactions with halogenated ethenes were investigated experimentally and computationally. The rate constants for the reactions of OH radicals with (E)-CFCl=CFCl (k1), (Z)-CFCl=CFCl (k2), and (E)-CHF=CHF (k3) were measured using flash and laser photolysis methods. The temporal profile of the OH radical was monitored by a laser-induced fluorescence technique. Kinetic measurements were carried out over the temperature range of 250−430 K. Arrhenius rate constants were determined to be k1 = (1.67 ± 0.06) × 10−12·exp[(140 ± 10) K/T], k2 = (1.75 ± 0.04) × 10−12·exp[(140 ± 10) K/T], and k3 = (3.99 ± 0.15) × 10−12·exp[(260 ± 10) K/T] cm3 molecule−1 s−1. The quoted uncertainties are 95% confidence levels and do not include systematic errors. Infrared absorption spectra were measured at room temperature. The atmospheric lifetimes and the global warming potentials of (E)-CFCl=CFCl, (Z)-CFCl=CFCl, and (E)-CHF=CHF were estimated to be 4.3, 4.2, and 1.2 days and 0.035, 0.036, and 0.0056, respectively. The ozone depletion potentials of (E)-CFCl=CFCl and (Z)-CFCl=CFCl were determined to be 0.00011 and 0.00010, respectively. The photochemical ozone creation potentials of the halogenated ethenes were less than 1/4 that of ethene. In addition, the (E)/(Z) differences in the energy and IR spectra of the CFCl=CFCl and CHF=CHF molecules were computationally examined. The reactivities of these halogenated ethenes toward OH radicals were investigated through the combination of DFT and ab initio computations. The rate constants calculated for the OH radical reactions of these halogenated ethenes showed reasonable agreement with the experimentally determined values. Our computational results for the CFCl=CFCl and CHF=CHF (E)/(Z) isomeric pairs indicated that the rate constants toward OH radicals are larger for the higher-energy geometrical isomers than for the lower-energy counterparts.

1. INTRODUCTION It is well known that the addition of an OH radical to a CC bond is generally more reactive than the abstraction of an H atom from a CH bond by the OH radical. Thus, compared to the corresponding saturated compound, an unsaturated compound is expected to exhibit increased reactivity toward OH radicals and a decreased atmospheric lifetime, global warming potential (GWP), and ozone depletion potential (ODP). For this reason, halogenated alkenes such as CF3CF=CH2 and (E)-CF3CH=CHCl have been developed as alternative refrigerants. However, halogenated alkenes may contribute to global warming when released into the atmosphere because they absorb in the infrared region of the atmospheric window due to the CF bonds. In addition, chlorinated compounds may deplete the stratospheric ozone layer by decomposing and releasing chlorine atoms into the stratosphere. Halogenated alkenes may also contribute to tropospheric ozone formation. The GWP depends on the decomposition rate in the atmosphere and the infrared absorption intensities of a compound. Because halogenated alkenes are decomposed mainly through OH radical addition to a CC bond, the atmospheric lifetime can be estimated from the reaction rate with OH radicals. In addition, the ODP and photochemical ozone creation potential (POCP) also depend on the atmospheric lifetime. Therefore, it is indispensable to evaluate © 2019 American Chemical Society

the reaction rates of halogenated alkenes with OH radicals and obtain the infrared spectra. In this work, the rate constants for reactions of (E)CFCl=CFCl, (Z)-CFCl=CFCl, and (E)-CHF=CHF with OH radicals and the infrared absorption spectra were measured. Consequently, the atmospheric lifetimes, GWPs, ODPs, and POCPs were estimated based on the reaction with OH radicals. The OH rate constants and infrared absorption spectra measurements of CHF=CHF (obtained from Asahi Glass) in our previous study1 were not made for the (E) isomer but for the (Z) isomer,2 by mistake of delivery of the sample. Presently, (E)CHF=CHF is a potential alternative for refrigerant R-410A,3 which is a blended refrigerant of CH2F2/CF3CHF2 (50:50 wt %). (E)-CFCl=CFCl and (Z)-CFCl=CFCl are not candidate replacement compounds. However, it may be useful to obtain accurate kinetic data for a variety of halogenated alkenes to develop an estimation method for the OH radical reaction rate constants. To examine the (E)/(Z) differences in energy and in the IR spectrum for the CFCl=CFCl and CHF=CHF molecules, computational investigations were performed. To interpret their reactivities toward OH radicals, the potential energy surfaces Received: March 15, 2019 Revised: May 17, 2019 Published: May 22, 2019 4834

DOI: 10.1021/acs.jpca.9b02454 J. Phys. Chem. A 2019, 123, 4834−4843

Article

The Journal of Physical Chemistry A

purified (E)-CFCl=CFCl and (Z)-CFCl=CFCl were 98.57 (the major impurity was the (Z) isomer with a content of 1.32%) and 99.38% (the major impurity was the (E) isomer with a content of 0.58%), respectively. The identification of the isomers has been carried out by comparison of theoretically and experimentally obtained IR spectra (see Section 3.2). Measurements of the reaction rates and the IR absorption spectra of (E)-CFCl=CFCl and (Z)-CFCl=CFCl were carried out using the purified samples. The purity of (E)-CHF=CHF (Asahi Glass) was found to be 99.74%, which is large enough that (E)-CHF=CHF was used for the measurements without further purification. The infrared spectra were measured using Fourier transform infrared spectroscopy (FTIR) between 400 and 4000 cm−1 at a spectral resolution of 1 cm−1. The sample gas was prepared to fill a sample at an appropriate pressure in the evacuated IR cell. Subsequently, dry N2 was added to the IR cell until the total pressure was approximately 760 torr.

along the reaction coordinates for OH radical addition to these halogenated ethenes were explored using density functional theory (DFT) and ab initio computations, and the reaction rates were computed. To compare the energies and reactivities of the (E) and (Z) isomeric pairs of these two olefins, computational results for the (Z) isomer of CHF=CHF are included in our theoretical discussion.

2. EXPERIMENTAL SECTION The experimental apparatus and procedure for the measurements of the reaction rate constants and IR spectra have been described previously.1,4,5 Briefly, the reaction rate constants were measured under pseudo-first-order conditions with a large excess of sample ((E)- or (Z)-CFCl=CFCl or (E)-CHF=CHF) relative to the initial concentration of OH radicals. OH radicals were produced by either the flash photolysis (FP) or laser photolysis (LP) method. The temporal profiles of OH radicals were measured using pulsed laser-induced fluorescence (LIF). For the FP method, H2O was directly photolyzed with pulsed light of a Xe flash lamp. For the LP method, two approaches were examined. First, OH radicals were produced by the reaction of O(1D) with H2O (LP-H2O method). Second, OH radicals were produced by the reaction of O(1D) with CH4 (LPCH4 method), which was a water-free OH production method. The O(1D) atoms were produced by photodissociation of N2O using an ArF excimer laser. Argon and helium were used as bath gases for the FP and LP methods, respectively. The flow rates of the components were measured and controlled by calibrated mass flow controllers (MFC). H2O vapor was supplied by bubbling a certain part of carrier gas (Ar or He) through a vessel filled with H2O at room temperature. The flow rate of H2O vapor was calculated from the flow rate of the carrier gas, temperature of H2O, and total pressure of the bubbler. The total pressure in the reactor was measured by a capacitance manometer and kept constant by an exhaust throttle valve located downstream of the reactor. The calibration of the MFC was performed by measuring the time−pressure relationship when sample vapor or gas was supplied to the vessel with known volume through the MFC. For gaseous materials, the calibration of the MFC was made with a gas meter or a soap-film flow meter. The concentration of the reactant was determined from the flow rate of halogenated ethenes and various gases, total pressure, and temperature of the reactor. The temperature of the reactor was measured by a thermocouple (Type K) at a location approximately 1−2 cm downstream from the probe laser beam. The experiments were repeated at intervals from several days to several months under a variety of flow conditions. The purity of the halogenated ethenes was determined using a gas chromatograph with a flame ionization detector. The analysis was carried out using various columns. CFCl=CFCl was obtained from Asahi Glass Cos., Ltd. as a mixture of the (E)/(Z) isomers. The purity of the mixture of CFCl=CFCl was approximately 95% (contents of (E) and (Z) isomers were approximately 56.4 and 38.4%, respectively). The mixture of CFCl=CFCl was purified and separated using a gas chromatograph. The apparatus and procedure for the sample purification have been described previously.6 Briefly, an evacuated sampling tube was charged with the sample vapor, and the charged sample was introduced into a column packed with Silicone DC 702 (Shimadzu). The middle fraction of the main peak was collected. This procedure was repeated hundreds of times to obtain sufficient amounts of the purified samples. The purities of the

3. RESULTS AND DISCUSSION 3.1. Kinetic Measurements. Rate constants for the reaction of OH radicals with (E)-CFCl=CFCl, (Z)CFCl=CFCl, and (E)-CHF=CHF were measured over a temperature range of 250−430 K. A sample decay plot for the OH radical and a plot of the observed pseudo-first-order rate constant kobs versus the (E)-CHF=CHF concentration are shown in Figure 1. Since the OH decay plots showed linear

Figure 1. Pseudo-first-order decay of OH radical for various (E)CHF=CHF concentrations. FP method, P = 200 torr, T = 298 K. [(E)CHF=CHF]/1015 molecule cm−3; (blue-green-lined circle), 0; (blue down-pointing triangle), 0.23; (pink up-pointing triangle), 0.46; (pinklined up-pointing triangle), 0.68; (red diamond), 0.91; (red-lined diamond), 1.13; (green-lined square), 1.35; (blue-green circle), 1.58; (green square), 1.72. The inset shows the plot of the observed pseudofirst-order rate constant kobs versus the (E)-CHF=CHF concentration.

relationships with small scatter, the pseudo-first-order decay rate constants (kobs) were derived from the slopes of each decay plot. The inset of Figure 1 shows the plot of kobs versus the (E)CHF=CHF concentration. The plot exhibited a linear relationship, and the rate constant for the reaction of OH with (E)CHF=CHF was derived from the slope using a linear least squares fit to the observed data. The value of kobs at zero reactant concentration (kd) is attributed to the diffusion of OH radicals from the viewing zone and hence depends on the experimental conditions. The value of kd was subtracted from kobs for each set 4835


Article

The Journal of Physical Chemistry A of plots of kobs versus the reactant concentration for various experimental conditions. Figure 2 shows kobs − kd versus the (E)-

were small. Thus, the systematic errors between the individual experimental techniques and the unexpected fluctuations of experimental conditions were negligible. Arrhenius parameters for the reactions of OH with the halogenated ethenes and the rate constants at 298 K derived from the Arrhenius rate parameters are shown in Table 1. Experimentally determined rate constants for OH with (E)-CFCl=CFCl, (Z)-CFCl=CFCl, and (E)-CHF=CHF have not been reported previously. 3.2. Measurement of IR Absorption Spectra. The infrared absorption cross sections were obtained from an average of 8 to 11 spectra of different sample partial pressures. The infrared absorption spectra of the halogenated ethenes between 400 and 2500 cm−1 at approximately 298 K in 760 torr N2 are shown in Figure 4. The infrared absorption spectra of (E)-CFCl=CFCl, (Z)-CFCl=CFCl, and (E)-CHF=CHF measured over the partial pressure ranges of 1.0−4.6, 1.1−4.3, and 1.0−3.8 torr, respectively, obeyed the Beer−Lambert law. Infrared absorption band strengths and the digitized infrared spectra for halogenated ethenes are available in Table 2 and in Table S11. In Table 2, the error limits are at the 95% confidence level from the integrated absorption cross section of individual spectra for different concentrations. The infrared absorption spectra of (E)-CFCl=CFCl and (Z)CFCl=CFCl between 1080 and 1300 cm−1 are shown in the inset of Figure 4. The weak absorption peak between 1100 and 1190 cm−1 for the (E) isomer was attributed to the (Z) isomer (the content of the (Z) isomer was 1.32%). Furthermore, the weak absorption peak between 1190 and 1250 cm−1 of the (Z) isomer was attributed to the (E) isomer (the content of the (E) isomer was 0.58%). Thus, we obtained the total absorption band strengths of (E)-CFCl=CFCl and (Z)-CFCl=CFCl at 400− 1100 and 1190−2000 cm−1 and at 400−1190 and 1250−2000 cm−1, respectively. The results are listed in Table 2. A comparison with previously reported IR absorption spectra of (E)-CFCl=CFCl, (Z)-CFCl=CFCl, and (E)-CHF=CHF is not possible because none is available. In addition, calculations of the IR spectra were carried out in the same manner as described in our previous paper.4 The geometry optimizations of the molecules and their frequency calculations were carried out using the DFT M062X functional and the aug-cc-pVTZ basis set. The calculated vibrational frequencies were scaled using the factors prescribed by Laury et al.7 More specifically, factors of 0.9698 and 0.9574 were applied for scaling the lower (below 1000 cm−1) and the higher frequencies, respectively. Satisfactory agreement was obtained between the calculated and experimentally measured IR spectra (see Figure 4). The calculations indicated that the IR spectra of the (E) and (Z) isomers can be easily distinguished for the CFCl=CFCl and CHF=CHF geometrical isomer pairs. 3.3. Atmospheric Implications. The atmospheric lifetimes of the halogenated ethenes were estimated using the reaction rates measured in this study. According to Wallington et al.,8 for species with lifetimes between 1 day and 1 year, a diurnally averaged OH of 1 × 106 molecules cm−3 is used with the OH rate coefficient at 298 K. Table 3 lists the atmospheric lifetimes with respect to the reaction with OH radicals, which were estimated using the same way as reported by Wallington et al.8 Here, the reaction rates at 298 K were obtained from the Arrhenius rate parameters listed in Table 1. Radiative efficiencies (RE) for the halogenated ethenes were estimated from the infrared spectra using a method based on the well-mixed model reported by Hodnebrog et al.9 Table 3 lists the REs for (E)-CFCl=CFCl, (Z)-CFCl=CFCl, and (E)-

Figure 2. Plot of the pseudo-first-order rate constants corrected for background values, kobs − kd versus the (E)-CHF=CHF concentration. FP method. (Blue down-pointing triangle), 250 K × 2.0; (green uppointing triangle), 298 K × 1.5; (black circle), 375 K; (red diamond), 430 K × 0.5.

CHF=CHF concentration for various temperatures. The plots show linear relationships. In all cases, the OH decay behavior and the linearity and the scatter of kobs − kd versus the reactant concentration were similar to those shown in Figures 1 and 2. The rate constants obtained in this study and the detailed information about the experimental conditions are shown in the Supporting Information (Tables S1−S3). The error limits are at the 95% confidence level derived from the linear least squares fit of kobs − kd versus reactant concentration, and systematic errors were not considered. The systematic errors in our experiments were estimated to be less than ±10% and were mainly caused by the accuracy of the concentration measurements. The systematic error was estimated from the sum of errors of MFCs, pressure transducer, and thermocouple. As shown in Tables S1− S3, the reaction rate constants were found to be independent of pressure in the range examined. Arrhenius plots of the reaction rates are shown in Figure 3. The Arrhenius plots showed linear relationships in the temperature range examined. The differences between the results obtained by the different methods

Figure 3. Arrhenius plot for the reactions of OH with CFCl=CFCl isomers and (E)-CHF=CHF. The solid lines represent the least squares fit to our data. The error bars are at the 95% confidence level and do not include systematic errors. 4836


Article

The Journal of Physical Chemistry A Table 1. Arrhenius Parameters for Reactions of OH with CFCl=CFCl Isomers and (E)-CHF=CHFa sample

A × 1012, cm3 molecule−1 s−1

E/R, K

k298 × 1012, cm3 molecule−1 s−1

(E)-CFCl=CFCl (Z)-CFCl=CFCl (E)-CHF=CHF

1.67 ± 0.06 1.75 ± 0.04 3.99 ± 0.15

−140 ± 10 −140 ± 10 −260 ± 10

2.67 ± 0.02 2.76 ± 0.01 9.37 ± 0.06

a

The errors represent 95% confidence levels obtained from nonlinear least squares analysis and do not include systematic errors.

CHF=CHF estimated using a 1 cm−1 resolution model. Hodnebrog et al.9 presented a method for estimating the radiative efficiency of very short-lived compounds based on the lifetime correction. The lifetime-corrected radiative efficiencies are listed in Table 3, which decreased by factors of 0.050, 0.049, and 0.016 for (E)-CFCl=CFCl, (Z)-CFCl=CFCl, and (E)CHF=CHF, respectively, compared to those obtained using the well-mixed gas approach. The global warming potentials for the 100 year time-horizon (GWP100) of the halogenated ethenes using the lifetime-corrected radiative efficiencies are listed in Table 3. The GWP100 values of the halogenated ethenes were less than 1, and the influence on the climate change by these compounds seems to be negligible. Patten and Wuebbles10 evaluated the ozone depleting potential (ODP) of (E)-CF3CH=CHCl to be 0.00034 using a 3D atmospheric model. They used the OH radical reaction rate constant of k((E)-CF 3 CH=CHCl) = 4.4 × 10 −13 cm 3 molecule−1 s−1 at T = 295 K reported by Sulbaek Andersen et al.,11 which was the only data available at that time. After, Gierczak et al.12 and Orkin et al.13 reported a temperaturedependent OH radical reaction rate constant for (E)CF3CH=CHCl. Based on the results reported by Gierczak et al.12 and Orkin et al.,13 Burkholder et al.14 recommended an OH radical rate constant of k((E)-CF3CH=CHCl) = 9.0 × 10−13· exp[−280 K/T]. Based on the recommended value proposed by Burkholder et al.,14 the OH radical rate constant at T = 272 K is 3.22 × 10−13 cm3 molecule−1 s−1, which is approximately 27% smaller than the OH radical rate constant reported by Sulbaek Andersen et al.11 As mentioned by Gierczak et al.,12 the ODPs of short-lived compounds, such as (E)-CF3CH=CHCl, depend not only on their atmospheric lifetime but also on the season and location of their emission. Therefore, model calculations are required to evaluate the ODPs of short-lived compounds. However, a simple procedure to estimate the ODP seems to be also valuable. In a previous report,4 we used 0.00047 as the modified ODP of (E)-CF3CH=CHCl based on the difference in the rate constants reported by Sulbaek Andersen et al.11 and recommended by Burkholder et al.13 Using the modified ODP of (E)-CF3CH=CHCl, we estimated the ODPs of (E)CFCl=CFCl and (Z)-CFCl=CFCl using the following simple scaling procedure

Figure 4. IR absorption cross sections of CFCl=CFCl and CHF=CHF isomers in 760 torr N2 measured by FTIR at a 1 cm−1 resolution. The inset shows IR absorption cross sections of (E)-CFCl=CFCl and (Z)CFCl=CFCl between 1080 and 1300 cm−1. Thin lines represent the radiative forcings reported by Hodnebrog et al.9 at 1 cm−1 resolution. Red lines represent calculated cross sections. Measured IR absorption cross section of (Z)-CHF=CHF taken from our previous report,1,2 plotted for comparison. Digitized spectra are available in the Supporting Information.

Table 2. Integrated Infrared Absorption Band Strengths for (E)-CFCl=CFCl, (Z)-CFCl=CFCl, and (E)-CHF=CHFa sample

integration range, cm−1

band strengths, 10−18 cm2 molecule−1 cm−1

(E)-CFCl=CFCl

820−915 1190−1250 400−1100, 1190−2000 920−1020 1100−1190 1660−1740 400−1190, 1250−2000 750−1000 1100−1200 1245−1310 400−2000

24.76 ± 0.11 39.05 ± 0.14 67.32 ± 0.34 24.31 ± 0.17 45.95 ± 0.27 3.02 ± 0.02 76.03 ± 0.68 10.95 ± 0.21 45.74 ± 0.23 2.67 ± 0.03 61.74 ± 0.58

(Z)-CFCl=CFCl

(E)-CHF=CHF

ODP = ODP1233zd(E) ×

M w1233zd(E) Mw

×

τ τ1233zd(E)

×

n n1233zd(E) (1)

where Mw, τ, and n are the molecular weight, lifetime, and number of Cl atoms contained in the compound, respectively, and the subscript 1233zd(E) denotes (E)-CF3CH=CHCl. The results are listed in Table 3, and the ODPs of the CFCl=CFCl isomers are less than 1/4 that of (E)-CF3CH=CHCl. Hence, their contributions to stratospheric ozone depletion are expected to be negligible. Recently, Jenkin et al.15 reported a method for estimating POCPs. According to the method reported by Jenkin et al.15 we

a

The error limits are at 95% confidence levels obtained from the integrated absorption cross section of individual spectra with different concentrations.

4837


Article


Table 3. Atmospheric Lifetimes, Radiative Efficiencies (RE), GWPs, and ODPs of CFCl=CFCl Isomers and (E)-CHF=CHF sample

lifetime, days

RE,a W m−2 ppb−1

RE (lifetime corr.),b W m−2 ppb−1

GWP100

ODP

(E)-CFCl=CFCl (Z)-CFCl=CFCl (E)-CHF=CHF

4.3 4.2 1.2

0.126 0.137 0.107

0.0063 0.0067 0.0017

0.035 0.036 0.0056

0.00011 0.00010

a RE: Radiative efficiency integrated in the 400−1100 and 1190−2000 cm−1 ranges for (E)-CFCl=CFCl, 400−1190 and 1250−2000 cm−1 ranges for (Z)-CFCl=CFCl, and 400−2000 cm−1 range for (E)-CHF=CHF. bRE (lifetime corr.): Lifetime-corrected radiative efficiency.

calculation technique developed by Hratchian and Schlegel.30,31 The frozen-core approximation was applied to the MP2, QCISD, and CCSD(T) calculations. The ultrafine grid was utilized for the DFT calculations. The detailed procedures for the energy evaluation through extrapolation of the single-point calculated energies to the basis set limit and additional comments regarding the rate constant computations are given in the Supporting Information. 3.4.2. Geometries of the CFCl=CFCl and CHF=CHF Molecules. The geometrical parameters optimized at various levels of theory are collected in Tables S4 and S5 for CFCl=CFCl and CHF=CHF, respectively. The optimized geometrical parameters were rather insensitive to the utilized computational levels. However, the MP2-optimized geometrical parameters showed small but systematic changes with the increase of the size index of the utilized correlation consistent basis sets. The plots of the MP2-optimized parameters against the index of the basis sets suggested that convergence was achieved for the bond lengths and angles at the basis set limit. Examples of the convergence of the CF bond lengths in the CHF=CHF molecule are illustrated in Figure S1. By fitting the MP2-optimized geometrical values to a simple exponential function of the index of the basis set size, the MP2-optimized geometrical values were extrapolated to the basis set limit. We obtained our best estimates for the geometrical parameters through extrapolation in this manner. Extensive experimental measurements have been reported regarding the geometries of the (E) and (Z) isomers of the CHF=CHF molecule.32,33 Table 4 shows our best estimates for the geometrical parameters of CHF=CHF with the experimentally determined values. The deviations of the MP2 extrapolated estimates from the experimental values were around 0.001 Å for the bond lengths and were less than 0.3° for the bond angles. The differences in the geometrical parameters between the (E) and (Z) isomers of CHF=CHF are noteworthy (Table 4). The (E)/(Z) difference of the CC bond length was quite small, and the signs of the difference between (E) and (Z) ((E) − (Z)) were opposite for the theoretical and experimental values. Both the theoretical and experimental values indicate that the CH bond lengthens slightly when transitioning from the (Z) isomer to the (E) isomer. A larger (E)/(Z) difference is apparent in the CF bond length. The CF bond in the (E) isomer was longer by 0.005−0.006 Å than that in the (Z) isomer. The bond angles of CCH and CCF in the (Z) isomer were nearly identical at around 122°. Meanwhile, the CCH bond angle in the (E) isomer was around 5° larger than the C CF bond angle. These trends in the (E)/(Z) geometrical differences were observed irrespective of the computational levels used (Table S5). To the best of our knowledge, no experimental measurements have been reported on the geometrical parameters for the (E)/ (Z) isomers of the CFCl=CFCl molecule. Our computational estimates for the geometrical parameters of the CFCl=CFCl

calculated the POCPs of (E)-CFCl=CFCl, (Z)-CFCl=CFCl, and (E)-CHF=CHF to be 5.5, 5.5, and 25.0, respectively, for multiday north-west European conditions and 5.1, 5.2, and 27.3, respectively, for single-day USA urban conditions. As a result, the POCPs of the halogenated ethenes studied in this work were less than approximately 1/4 that of ethene (POCPethene = 100, by definition). Recently, Wallington et al.8 studied the GWPs, ODPs, and POCPs of short-chain haloolefins and reported that they were negligible. The results of the present study are consistent with those of Wallington et al.8 3.4. Computational Results. 3.4.1. Computational Procedure. The geometries of the (E) and (Z) isomers of the CFCl=CFCl and CHF=CHF molecules were optimized using DFT [B3LYP16,17 and M062X18,19] and ab initio [MP2,20,21 and QCISD22] calculations. Correlation consistent basis sets23 were employed. For accurate energy evaluation, single-point energy evaluations at the MP2 and CCSD(T)22 levels were performed at the M062X/aug-cc-pVTZ-optimized geometries. The basis set limit energies at the CCSD(T) level were estimated using the extrapolation procedures proposed by Feller24 and Helgaker et al.25 The reaction coordinates for the OH radical addition to the CFCl=CFCl or CHF=CHF molecule were explored with calculations at the M062X/aug-cc-pVTZ level. The transition state structures were optimized at this level, after which intrinsic reaction coordinate (IRC) calculations26 were performed. To accurately evaluate the energies of the stationary points along the reaction coordinates, MP2 and CCSD(T) level single-point calculations were applied to the M062X/aug-cc-pVTZoptimized geometries. The unrestricted Hartree−Fock (UHF) wave functions for the transition states of the CFCl = CFCl and CHF=CHF reactions were found to be significantly spincontaminated. The ideal value is 0.75 for a spin doublet,27 but the actual values of the UHF wave functions for the transition states were 0.9−1.0. Hence, we utilized the restrictedopen-shell scheme for the MP2 and CCSD(T) calculations, and more specifically, ROMP2 and ROCCSD(T) single-point calculations were carried out. The obtained single-point energies were extrapolated to the basis set limit to evaluate the relative energies of the stationary points. The rate constants for the OH radical addition to the olefins were calculated using the conventional transition state theory28 based on the following equation: k T QTS i ΔE yz zz k(T ) = Γ(T ) B expjjj− h Q R Q OH k RT { #

(2)

kB, h, and R are the Boltzmann, Planck, and gas constants, respectively. Meanwhile, Q#TS, QR, and QOH represent the partition functions of the transition state, reactant olefin, and OH radical, respectively, and ΔE is the reaction barrier height for the OH radical addition. The Gaussian software package29 was used for all the quantum mechanical calculations. We employed the IRC 4838


Article

The Journal of Physical Chemistry A Table 4. Geometrical Parameters of the (E) and (Z) Isomers of CHF=CHFa bond CC

CH

CF

CCH

CCF

parameter

(E)

(Z)

(E) − (Z)

theoryb expt.c theory − expt. theory expt. theory − expt. theory expt. theory − expt. theory expt. theory − expt. theory expt. theory − expt.

1.3227 1.324 −0.001 1.0768 1.078 −0.001 1.3398 1.339 0.001 125.2 125.1 0.1 119.5 119.8 −0.3

1.3237 1.323 0.001 1.0763 1.075 0.001 1.3336 1.334 0.000 122.4 122.5 −0.1 122.4 122.3 0.1

−0.0010 0.001

Table 5. Calculated Potential Energy Differences (ΔEe) between the (E) and (Z) Isomers of CFCl=CFCl and CHF=CHF Moleculesa

0.0005 0.003 0.0062 0.005

computational levelb

CFCl=CFCl

CHF=CHF

B3LYP/aug-cc-pVTZ M062X/aug-cc-pVTZ MP2/aug-cc-pVDZ MP2/aug-cc-pVTZ MP2/aug-cc-pVQZ MP2/aug-cc-pV5Z QCISD/aug-cc-pVTZ best estimatec

−0.74 −0.71 −0.59 −0.38 −0.32 −0.27 −0.55 −0.34 (−0.32)

0.98 0.86 1.04 1.22 1.24 1.23 1.03 1.01 (0.84)

Energy differences are given in the unit of kcal mol−1. Positive values indicate that the (Z) isomer is lower in energy than the (E) isomer. b Except for the best estimate, the geometry optimization and energy evaluation were performed at the same computational level. cThe geometries of the (E) and (Z) isomers of CFCl=CFCl and CHF=CHF were optimized at the M062X/aug-cc-pVTZ level. The basis set limit energies at the CCSD(T) level were estimated through an extrapolation procedure using the HF, MP2, and CCSD(T) singlepoint energies. The details of the extrapolation procedure are described in the Supporting Information. The calculated values for the (E)/(Z) enthalpy differences at 298 K are given in parentheses. The unscaled M062X vibrational frequencies were employed for computing the enthalpy contributions. a

2.8 2.6 −2.9 −2.5

a

Bond lengths (CC, CH, and CF) and bond angles (CC H and CCF) are given in units of Å and degrees, respectively. b The bond lengths and angles were optimized at the MP2 level with the correlation consistent basis sets (aug-cc-pVXZ, X = T, Q, 5), after which they were extrapolated to the basis set limit (see the text). The extrapolated values are provided. cThe experimental values are taken from the paper by Craig et al.33

calculated energies of the (Z) isomer were lower than those of the (E) isomer (Table 5). Craig et al.36,38 estimated the electronic energy difference between the (E) and (Z) isomers to be 1080 ± 120 cal mol−1. Their estimate was derived from the experimentally determined enthalpy values and the spectroscopically obtained vibrational energies. Our MP2 calculations slightly overestimated the (E)/(Z) energy difference. However, the best estimate for the electronic energy (potential energy) difference between the (E) and (Z) isomers was 1.01 kcal mol−1 (Table 5), which is sufficiently close to the value reported by Craig et al.36,38 In addition, our estimate for the enthalpy difference between the (E)/(Z) isomers was 0.84 kcal mol−1 at 298 K. The corresponding experimentally derived value was reported as 928 ± 28 cal mol−1.37,38 The cis effect has been discussed extensively in several research papers,39−42 but its origin remains elusive. Certainly, the (E)/(Z) energy difference of the CHF=CHF molecule, as well as the abovementioned geometrical features of this molecule, is not understandable from the standpoint of the electrostatically or sterically repulsive fluorine−fluorine interactions. Some other factors should be taken into account for interpreting the cis effect. However, a detailed discussion regarding the cis effect is beyond the scope of this paper. 3.4.4. Reaction Energy Profiles for OH Radical Addition. We located the transition states for the OH radical addition to the olefins CFCl=CFCl and CHF=CHF. Only one transition state was located for the OH radical addition to the (Z) isomer of CHF=CHF. For the other cases, two transition states, in which the directions of the OH radical differed, were found (Figure 5). The IRC calculations starting from the two transition states for the (E) isomer of CFCl=CFCl reached identical reactant complexes. Similarly, the two transition states for the (E)CHF=CHF reaction were led to the same reactant complex as well. All the transition states were computed to be lower in energy than the reactants. The structures of the transition states were close to those of the reactants; namely, early transition states are

molecule are shown in Table S6. The (E)/(Z) differences in bond lengths and angles of the CFCl=CFCl molecule were much smaller than those of the CHF=CHF molecule. 3.4.3. (E)/(Z) Energy Differences of the CFCl=CFCl and CHF=CHF. In 1965, Craig and Evans34 reported an experimental estimate for the enthalpy change of the (E)/(Z) isomerization of the CFCl=CFCl molecule of nearly zero. Correspondingly, our calculated results suggested that there were relatively small (less than 1 kcal mol−1) (E)/(Z) energy differences, but the (E) isomer was calculated to be energetically more favorable than the (Z) isomer without exception (Table 5). Our best estimates for the electronic energy and enthalpy differences between the (E) and (Z) isomers of CFCl=CFCl were 0.34 and 0.32 kcal mol−1, respectively (see Table S10 for details). Meanwhile, the (E)/(Z) isomerization of the CHF=CHF molecule was investigated by Craig and Entemann,35 and their experimental results were reported in 1961. Interestingly, they revealed that the (Z) isomer of CHF=CHF was energetically more favorable than the (E) isomer.35 This phenomenon has been referred to as the “cis effect”.36,37 The cis effect is contrary to the “typical” cis−trans energy relationship such as that in 2butene. For 2-butene, the trans, that is, (E), isomer is energetically more favorable than the cis, that is, (Z), isomer. The energetic preference of the trans isomer for 2-butene is interpreted to be mainly due to steric repulsion between the methyl groups in the cis isomer. The fluorine atom is more electronegative and sterically larger than the hydrogen atom, and the distance between the two fluorine atoms is shorter in the (Z) isomer than in the (E) isomer for CHF=CHF. Thus, the (Z) isomer of CHF=CHF was expected to undergo larger electrostatic and steric destabilization than the (E) counterpart. Nevertheless, the experimental measurements indicated that the (Z) isomer of CHF=CHF is energetically lower than the (E) counterpart. Our calculations for CHF=CHF successfully reproduced the cis effect. Regardless of the utilized computational levels, the 4839


Article


Figure 5. Structures optimized at the M062X/aug-cc-pVTZ level. The carbon, oxygen, fluorine, chlorine, and hydrogen atoms are shown by dark gray, red, light blue, green, and light gray balls, respectively. The C···O bond lengths and the dihedral angles about CC···OH in the transition states are given in the units of Å and degrees, respectively. The energy relative to the reactants for each transition state is given in Table 6.

suggested (Figure 5). Corresponding to the Hammond postulate,43 OH radical addition reactions were found to be highly exothermic. The calculated values for the exothermicities ranged from 38 to 44 kcal mol−1 (Table 6). The structures of the reactant complexes and product radicals are shown in Figures S2 and S3, respectively.

Table 7. Calculated and Experimentally Determined Rate Constants for the Reactions of the (E) and (Z) Isomers of CFCl=CFCl and CHF=CHF with OH Radicals k × 1012 cm3 molecule−1 s−1 (E)

Table 6. Energies of the Stationary Points along the Reaction Coordinates for OH Radical Addition Reactionsa olefin

isomer

CFCl=CFCl

(E) (Z)

CHF=CHF

(E) (Z)

transition state

reactant complex

TS-1 TS-2 TS-1 TS-2 TS-1 TS-2 TS-1

−0.94b −0.81 −1.04 −0.90b −1.29

TS

product

−0.39 −0.31 −0.41 −0.41 −0.67 −0.73 −1.07

−43.81 −43.81 −43.72 −43.80 −38.34 −37.77 −37.84

Energies relative to the reactants are given in the unit of kcal mol−1. The energies of the stationary points were evaluated based on those extrapolated to the basis set limit. The procedure of the energy extrapolation is described in the Supporting Information. Energy values include the M062X/aug-cc-pVTZ calculated zero-point energies (ZPEs) (unscaled). bThe IRC calculations starting from the TS-1 and TS-2 of the (E) isomers of CFCl=CFCl and CHF=CHF led to the same reactant complexes (see the text). a

T, K

calculated

250 273 298 331 375 430

2.60 2.45 2.35 2.29 2.29 2.38

250 273 298 331 375 430

8.40 7.50 6.86 6.34 5.98 5.87

a

(Z) b

experimental

CFCl=CFCl 2.93 ± 0.03 2.79 ± 0.02 2.67 ± 0.02 2.55 ± 0.02 2.43 ± 0.02 2.31 ± 0.03 CHF=CHFc 11.0 ± 0.1 10.1 ± 0.1 9.37 ± 0.06 8.61 ± 0.06 7.86 ± 0.07 7.21 ± 0.09

calculated

a

experimentalb

3.06 2.86 2.73 2.65 2.63 2.71

3.01 ± 0.02 2.87 ± 0.02 2.76 ± 0.01 2.63 ± 0.01 2.51 ± 0.01 2.40 ± 0.02

7.99 6.74 5.84 5.10 4.53 4.19

9.29 ± 0.06 8.61 ± 0.04 8.02 ± 0.03 7.44 ± 0.03 6.86 ± 0.03 6.35 ± 0.04

a

Rate constants were calculated separately for the reaction path passing through each transition state. The calculated rate constants for each reaction path are given in Table S7. The calculated total rate constants are given here. bDerived from Arrhenius rate parameters. c Experimentally determined rate constant values for the (Z) isomer were taken from our previous paper.1,2

3.4.5. Calculation of the Rate Constants. The calculated rate constants for the OH radical addition to the (E) and (Z) isomers of CFCl=CFCl and CHF=CHF are given in Table 7, and their Arrhenius plots are shown in Figure S4. As compared with the experimentally determined values, our calculations suggested somewhat smaller rate constants for the reactions of CHF=CHF. The computed rate constants at 298 K were around 73% of experimentally determined ones. Meanwhile, the calculated rate constants for the reactions of CFCl=CFCl were quite close to the experimental values, but weak non-Arrhenius behavior was observed for the computational results. However, the experimental rate constants exhibited linear Arrhenius plots not only for the reactions of CHF=CHF but also for those of CFCl=CFCl (Figure 3 and Figure S4).

Our calculations did not necessarily succeed in reproducing the abovementioned experimental observations. As described in Section 3.4.1, we performed MP2 and CCSD(T) level singlepoint energy evaluations after M062X-level geometry optimizations to explore the potential energy surface for the OH addition to CFCl=CFCl and CHF=CHF. The combination of M062Xlevel geometry optimizations and high-level ab initio singlepoint energy evaluations has been applied to investigations on the mechanism, kinetics, and thermochemistry of atmospheric reactions of various fluorinated compounds.44−46 Nevertheless, it would be rather difficult to provide distinct discussions on the magnitude of the uncertainties of the theoretical rate constants in the present study and on the origins of the not very large but 4840


Article

The Journal of Physical Chemistry A Table 8. Calculated Values for the Deformation Energies and the Interaction Energies in the Transition Statesa deformation energyb

interaction energyc

olefin

isomer

transition state

M062X

(RO)CCSD(T)

M062X

(RO)CCSD(T)

CFCl=CFCl

(E)

TS-1 TS-2 TS-1 TS-2 TS-1 TS-2 TS-1

1.46 1.43 1.43 1.36 0.63 0.66 0.75

1.14 1.11 1.14 1.03 0.36 0.39 0.44

−3.67 −3.54 −3.73 −3.61 −3.50 −3.58 −3.95

−3.29 −3.20 −3.34 −3.19 −2.70 −2.83 −3.17

(Z) CHF=CHF

(E) (Z)

Energy values are given in the unit of kcal mol−1. Energy values were computed with the M062X/aug-cc-pVTZ and (RO)CCSD(T)/aug-cc-pVTZ level calculations at the M062X/aug-cc-pVTZ-optimized geometries. bThe destabilization energy due to deformation of the reactants in the transition states. cThe stabilization energy due to the interaction between the deformed reactants in the transition states. a

not negligible differences observed between the experiments and theory. However, the following experimentally observed reactivity trends were consistent with our calculated results. First, a weak negative temperature dependency was observed for the OH radical reactions of these olefins in the 250−430 K temperature range (Figure S4). Second, the rate constants for the (E)/(Z) isomeric pair of CHF=CHF were larger than those of CFCl=CFCl. Finally, the (E)/(Z) reactivity differences were found to be rather small in the measured temperature range (250−430 K) for these compounds, but the (Z) isomer of CFCl=CFCl and the (E) isomer of CHF=CHF were slightly more reactive than their isomeric counterparts. For CFCl=CFCl and CHF=CHF, the reactant complexes were found along the reaction coordinates of their OH radical addition reactions. The transition states, as well as the reactant complexes, were computed to be lower in energy than the reactants (Table 6). These characteristics of the reaction coordinates were directly related to the experimentally observed negative temperature dependencies of the OH radical addition. The energies of the transition states for the CFCl=CFCl reaction relative to the reactants were calculated to be less negative than those for the CHF=CHF reactions (Table 6). This result suggests that CFCl=CFCl has a lower reactivity than CHF=CHF. The transition states for the OH radical addition reaction consist of the slightly deformed reactants, that is, the slightly deformed OH radical and olefin. We evaluated the destabilization energies resulting from the deformation of the reactants in the transition states. In particular, the energy changes of the OH radical and the olefin accompanying their structural changes upon going from the equilibrium structures to the transition state structures were computed. Concomitantly, the stabilization energies in the transition states due to the interaction between the OH radical and olefin were evaluated. The transition states for the CFCl=CFCl reaction were shown to undergo a slightly greater destabilization due to the deformation of the reactants than those for the CHF=CHF reaction. Regarding the magnitude of the stabilization due to the interaction between the reactants, the differences between the transition states for the CFCl=CFCl reaction and those for the CHF=CHF reaction were found to be less significant (Table 8). Hence, the less negative relative energies of the transition states for the CFCl=CFCl reaction as compared with those for the CHF=CHF reaction are attributable mainly to the differences in the magnitude of the deformation of the reactants in the transition states. The structural changes that occur during the transition from the reactants to the transition states imply that the deformation of the reactants in the transition states is slightly larger for the

reactions of CFCl=CFCl than in those of CHF=CHF. The C C double bonds is lengthened more in the transition states for the reactions of CFCl=CFCl than in those for the reactions of CHF=CHF. In addition, the pyramidalization of the carbon atom being attacked is more advanced in the transition states for CFCl=CFCl reactions than in those for CHF=CHF reactions (Tables S8 and S9). Since hydrogen atoms in CHF=CHF have been replaced by chlorine atoms in CFCl=CFCl, it is quite reasonable that the steric repulsion in the transition states should be increased for the reactions of CFCl=CFCl than for those of CHF=CHF. The bulkiness of a chlorine atom compared to a fluorine atom was pointed out previously by Cometto et al.47 The (E)/(Z) reactivity differences of CFCl=CFCl and CHF=CHF toward OH radicals are not very pronounced. We cannot provide a clear explanation for the (E)/(Z) reactivity differences of these haloolefins presently. The (E)/(Z) reactivity differences toward OH radicals have been revealed for various haloolefins. In the present study, our experimental measurements and calculations indicated that higher-energy geometrical isomers, namely, the (Z) isomer for CFCl=CFCl and the (E) isomer for CHF=CHF, are slightly more reactive toward the OH radicals than their lower-energy isomers. Such (E)/(Z) reactivity trends for the OH radical reactions have been reported for several haloolefins, for example, CF 3 CF=CHF, 48 CF3CH=CHCl,12,49 CF3CF=CHCl,4 and CF3CH=CHCF3.50,51 However, the opposite (E)/(Z) reactivity trend has been observed for haloolefins, such as CHF 2 CF=CHCl, 4 CF3CF=CFCF3,52 and CHCl = CHCl.53 For these haloolefins, the higher-energy isomers have been reported to be less reactive than the lower-energy counterparts. Similar to CHF=CHF, the cis effect has been recognized for the (E)/(Z) energy difference of CHCl=CHCl. Experimental measurements indicated that the electronic energy of the (Z) isomer of CHCl=CHCl was lower by 720 ± 160 cal mol−1 compared to that of the (E) isomer.36

4. CONCLUSIONS The OH reaction rates and infrared absorption spectra of (E)CFCl=CFCl, (Z)-CFCl=CFCl, and (E)-CHF=CHF were measured. The estimated lifetimes due to the OH radical reactions of (E)-CFCl=CFCl, (Z)-CFCl=CFCl, and (E)CHF=CHF were 4.3, 4.2, and 1.2 days, respectively, and the GWP100 values were less than 1. The ODPs of the CFCl=CFCl isomers were approximately 1/4 that of (E)-CF3CH=CHCl. The POCPs of the halogenated ethenes were approximately 1/4 that of ethene. Thus, the halogenated ethenes studied in this work have negligible global warming, stratospheric ozone depletion, and photochemical ozone creation potentials. 4841


Article


ments and Correlation between Structure and Reactivity. J. Phys. Chem. A 2018, 122, 4593−4600. (2) Tokuhashi, K.; Takizawa, K.; Kondo, S. Correction to “Rate Constants for the Reactions of OH Radicals with Fluorinated Ethenes: Kinetic Measurements and Correlation between Structure and Reactivity”. J. Phys. Chem. A 2019, 123, 382−383. (3) Asahi Glass Co. Ltd. Working Medium for Heat Cycle, Composition for Heat Cycle System, and Heat Cycle System. International Patent No WO 2015/186557 A1, 2015. (4) Tokuhashi, K.; Uchimaru, T.; Takizawa, K.; Kondo, S. Rate Constants for the Reactions of OH Radical with the (E)/(Z) Isomers of CF3CF=CHCl and CHF2CF=CHCl. J. Phys. Chem. A 2018, 122, 3120−3127. (5) Tokuhashi, K.; Takizawa, K.; Kondo, S. Rate Constants for the Reactions of OH Radicals with CF3CX=CY2 (X = H, F, CF3, Y = H, F, Cl). J. Environ. Sci. Pollut. Res. 2018, 25, 15204−15215. (6) 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. (7) 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 Sets. J. Comput. Chem. 2011, 32, 2339−2347. The authors have reported separate scale factors for the high (>1000 cm−1) and low frequencies. To report scale factors to four places past the decimal is common practice, but which could overstate the accuracy of the scale factors. The root mean square errors of the M062X/aug-cc-pVTZ computational level were reported to be 40.7 and 15.90 cm−1 for high and low frequencies, respectively, for 40 molecules examined (8) 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. (9) 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. (10) 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. (11) Sulbaek Andersen, M. P.; Nilsson, E. J. K.; Nielsen, O. J.; Johnson, M. S.; Hurley, M. D.; Wallington, T. J. Atmospheric Chemistry of trans-CF3CHCHCl: Kinetics of the Gas-Phase Reactions with Cl Atoms, OH Radicals, and O3. J. Photochem. Photobiol., A. 2008, 199, 92−97. (12) Gierczak, T.; Baasandorj, M.; Burkholder, J. B. OH + (E)- and (Z)-1-Chloro-3,3,3-trifluoropropene-1 (CF3CHCHCl) Reaction Rate Coefficients: Stereoisomer-dependent Reactivity. J. Phys. Chem. A. 2014, 118, 11015−11025. (13) Orkin, V. L.; Martynova, L. E.; Kurylo, M. J. Photochemical Properties oftrans-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. (14) 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: Pasadena, 2015 (http://jpldataeval.jpl.nasa. gov).

Our theoretical calculations successfully reproduced the wellknown cis effect of the CHF=CHF molecule; the (Z) isomer was calculated to be lower in energy than the (E) isomer. For the CFCl=CFCl molecule, the energy of the (E) isomer was found to be slightly lower than that of the (Z) isomer. The computed rate constants for the OH radical reactions of CFCl=CFCl and CHF=CHF showed reasonable agreement with the experimentally determined values. Our computational results for the OH radical reactions indicated that the higher-energy geometrical isomer exhibited greater reactivity than the lower-energy isomer for the CFCl=CFCl and CHF=CHF isomeric pairs. In addition, the transition states for OH radical addition to the CFCl=CFCl molecule were shown to undergo slightly larger steric repulsion than those for OH radical addition to the CHF=CHF molecule. This computational suggestion should be related, at least partially, to our experimental observation that the reactivity of CFCl=CFCl toward the OH radicals is lower than that of CHF=CHF.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpca.9b02454. Tables of experimental conditions and the OH radical reaction rate constants of (E)-CFCl=CFCl, (Z)CFCl=CFCl, and (E)-CHF=CHF; geometrical parameters of CFCl=CFCl and CHF=CHF optimized at various computational levels; calculated rate constant values; comparison of geometrical parameters between the reactants and the transition states for OH addition reactions; plots of the MP2-optimized CF bond lengths against the basis set index; structures of the reactant complexes and product radicals; the Cartesian coordinates of the structures optimized at the M062X/aug-ccpVTZ level; the description of extrapolation procedure of the single-point calculated energies to the basis set limit; the computed energy values utilized for the extrapolation of the basis set limit; additional comments regarding the rate constant calculations; the complete description of ref 29 (PDF) Digitized infrared cross section spectra for halogenated ethenes (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +81-29-861-9441. Fax: +81-29-861-4770. ORCID

Kenji Takizawa: 0000-0002-3642-5735 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was financially supported by the New Energy and Industrial Technology Development Organization (NEDO). We greatly appreciate computational facilities generously provided by the Tsukuba Advanced Computing Center.

■

REFERENCES

(1) Tokuhashi, K.; Takizawa, K.; Kondo, S. Rate Constants for the Reactions of OH Radicals with Fluorinated Ethenes: Kinetic Measure4842


Article

The Journal of Physical Chemistry A (15) Jenkin, M. E.; Derwent, R. G.; Wallington, T. J. Photochemical Ozone Creation Potentials for Volatile Organic Compounds: Rationalization and Estimation. Atmos. Environ. 2017, 163, 128−137. (16) Becke, A. D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648−5652. (17) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B 1988, 37, 785−789. (18) Zhao, Y.; Truhlar, D. G. Density Functionals with Broad Applicability in Chemistry. Acc. Chem. Res. 2008, 41, 157−167. (19) 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 four M06-Class Functionals and 12 Other Functionals. Theor. Chem. Acc. 2008, 120, 215− 241. (20) Møller, C.; Plesset, M. S. Note on an Approximation Treatment for Many-Electron Systems. Phys. Rev. 1934, 46, 618−622. (21) Head-Gordon, M.; Pople, J. A.; Frisch, M. J. MP2 Energy Evaluation by Direct Methods. Chem. Phys. Lett. 1988, 153, 503−506. (22) Pople, J. A.; Head-Gordon, M.; Raghavachari, K. Quadratic Configuration Interaction. A General Technique for Determining Electron Correlation Energies. J. Chem. Phys. 1987, 87, 5968−5975. (23) Dunning, T. H., Jr. Gaussian Basis Sets for Use in Correlated Molecular Calculations. I. The Atoms Boron through Neon and Hydrogen. J. Chem. Phys. 1989, 90, 1007−1023. (24) Feller, D. The Use of Systematic Sequences of Wave Functions for Estimating the Complete Basis Set, Full Configuration Interaction Limit in Water. J. Chem. Phys. 1993, 98, 7059−7071. (25) Helgaker, T.; Klopper, W.; Koch, H.; Noga, J. Basis-Set Convergence of Correlated Calculations on Water. J. Chem. Phys. 1997, 106, 9639−9646. (26) Fukui, K. The Path of Chemical Reactions - the IRC Approach. Acc. Chem. Res. 2002, 14, 363−368. (27) Szabo, A.; Ostlund, N. S. Modern Quantum Chemistry Introduction to Advanced Electronic Structure Theory; Macmillan Publishing Co., Inc.: New York, 1982. (28) Eyring, H. The Activated Complex in Chemical Reactions. J. Chem. Phys. 1935, 3, 107−115. (29) 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 09, Revision D.01; Gaussian Inc.: Wallingford, CT, 2009. (30) Hratchian, H. P.; Schlegel, H. B. Accurate Reaction Paths Using a Hessian Based Predictor−corrector Integrator. J. Chem. Phys. 2004, 120, 9918−9924. (31) Hratchian, H. P.; Schlegel, H. B. Using Hessian Updating to Increase the Efficiency of a Hessian Based Predictor-Corrector Reaction Path Following Method. J. Chem. Theory Comput. 2005, 1, 61−69. (32) Feller, D.; Craig, N. C.; Groner, P.; McKean, D. C. Ab Initio Coupled Cluster Determination of the Equilibrium Structures of cisandtrans-1,2-Difluoroethylene and 1,1-Difluoroethylene. J Phys. Chem. A 2011, 115, 94−98. (33) Craig, N. C.; Groner, P.; McKean, D. C.; Tubergen, M. J. Equilibrium Structures for Thecis Andtrans Isomers of 1,2-Difluoroethylene and The Cis,Trans Isomer of 1,4-Difluorobutadiene. Int. J. Quant. Chem. 2003, 95, 837−852. (34) Craig, N. C.; Evans, D. A. Infrared and Raman Spectra of cis- and trans-1,2-Dichloro-1,2-Difluoroethylene. J. Am. Chem. Soc. 1965, 87, 4223−4230. (35) Craig, N. C.; Entemann, E. A. Thermodynamics of Cis-Trans Isomerizations. The 1,2-Difluoroethylenes. J. Am. Chem. Soc. 1961, 83, 3047−3050. (36) Craig, N. C.; Piper, L. G.; Wheeler, V. L. Thermodynamics of cistrans Isomerizations. II. 1-Chloro-2-Fluoroethylenes, 1,2-Difluorocyclopropanes, and Related Molecules. J. Phys. Chem. 1971, 75, 1453− 1460.

(37) Kaiser, E. W.; Pierce, D. S. Study of the Thermodynamics (Thermal and Cl Catalyzed) and Kinetics of the cis and trans I s o m er i z a t i o n s o f C F 3 C F = C H F , C F 3 C H = C H C F 3 , a n d CH3CH=CHCH3 in 100−950 Torr of N2 Diluent at 296−875 K: Effect of F and CF3 Substitution on the Isomerization Process Including the Fluorine “Cis Effect”. J. Phys. Chem. A 2015, 119, 9000−9017. (38) Craig, N. C.; Overend, J. Vibrational Assignments and Potential Constants for Cis- and Trans-1, 2-Difluoroethylenes and Their Deuterated Modifications. J. Chem. Phys. 1969, 51, 1127−1142. (39) Chaudhuri, R. K.; Hammond, J. R.; Freed, K. F.; Chattopadhyay, S.; Mahapatra, U. S. Reappraisal of Cis Effect in 1,2-Dihaloethenes: An Improved Virtual Orbital Multireference Approach. J. Chem. Phys. 2008, 129, No. 064101. (40) Yamamoto, T.; Kaneno, D.; Tomoda, S. The Origin of cis Effect in 1,2-Dihaloethenes: The Quantitative Comparison of Electron Delocalizations and Steric Exchange Repulsions. Bull. Chem. Soc. Jpn. 2008, 81, 1415−1422. (41) Jenkins, S.; Kirk, S. R.; Rong, C.; Yin, D. The cis-Effect Using the Topology of the Electronic Charge Density. Mol. Phys. 2013, 111, 793− 805. (42) Banerjee, D.; Ghosh, A.; Chattopadhyay, S.; Ghosh, P.; Chaudhuri, R. K. Revisiting the ‘cis-Effect’ in 1,2-Difluoro Derivatives of Ethylene and Diazene Using Ab Initio Multireference Methods. Mol. Phys. 2014, 112, 3206−3224. (43) Hammond, G. S. A Correlation of Reaction Rates. J. Am. Chem. Soc. 1955, 77, 334−338. (44) Ramanjaneyulu, C.; Rajakumar, B. Kinetic Parameters for the Reaction of OH Radical with cis-CHF=CHCHF 2 , transCHF=CHCHF2, CF2=CHCHF2 and CF2=C=CHF: Hybrid Meta DFT and CVT/SCT/ISPE Calculations. J. Fluorine Chem. 2015, 178, 266−278. (45) Vereecken, L.; Crowley, J. N.; Amedro, D. Theoretical Study of the OH-initiated Atmospheric Oxidation Mechanism of Perfluoro Methyl Vinyl Ether, CF3OCF=CF2. Phys. Chem. Chem. Phys. 2015, 17, 28697−28704. (46) Baidya, B.; Lily, M.; Chandra, A. K. Theoretical Insight into the Kinetics of H-Abstraction Reaction of CHF2CH2OH with OH Radical, Atmospheric Lifetime and Global Warming Potential. ChemistrySelect 2018, 3, 6136−6144. (47) Cometto, P. M.; Taccone, R. A.; Nieto, J. D.; Dalmasso, P. R.; Lane, S. I. Kinetic Study of OH Radical Reactions with CF3CCl=CCl2, CF3CCl=CClCF3 and CF3CF=CFCF3. ChemPhysChem 2010, 11, 4053−4059. (48) 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. (49) Andersen, 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. (50) Baasandorj, M.; Ravishankara, A. R.; Burkholder, J. B. Atmospheric Chemistry of (Z)-CF3CH=CHCF3: OH Radical Reaction Rate Coefficient and Global Warming Potential. J. Phys. Chem. A. 2011, 115, 10539−10549. (51) Baasandorj, M.; Marshall, P.; Waterland, R. L.; Ravishankara, A. R.; Burkholder, J. B. Rate Coefficient Measurements and Theoretical Analysis of the OH + (E)-CF3CH=CHCF3 Reaction. J. Phys. Chem. A. 2018, 122, 4635−4646. (52) Orkin, V. L.; Poskrebyshev, G. A.; Kurylo, M. J. Rate Constants for the Reactions between OH and Perfluorinated Alkenes. J. Phys. Chem. A. 2011, 115, 6568−6574. (53) Zhang, Z.; Liu, R.; Huie, R. E.; Kurylo, M. J. A Gas-Phase Reactivity Study of Hydroxyl Radicals with 1,1-Dichloroethene and cisand trans-1,2-Dichloroethene Over the Temperature Range 240-400 K. J. Phys. Chem. 1991, 95, 194−196.

4843


(Z

Recommend Documents