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Rate Coefficient Measurements and Theoretical Analysis of the OH + (E) CF3CH=CHCF Reaction 3

Munkhbayar Baasandorj, Paul Marshall, Robert L. Waterland, Akkihebbal R. Ravishankara, and James B. Burkholder J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.8b02771 • Publication Date (Web): 25 Apr 2018 Downloaded from http://pubs.acs.org on April 26, 2018

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The Journal of Physical Chemistry

1 2

Rate Coefficient Measurements and Theoretical Analysis of the OH + (E)-CF3CH=CHCF3 Reaction

3 4 5 6 7 8 9 10 11 12 13 14 15

Munkhbayar Baasandorj,1,2,# Paul Marshall,3 Robert L. Waterland,4,& A.R. Ravishankara,1,$ and James B. Burkholder1* 1 2 3 4

Earth System Research Laboratory, Chemical Sciences Division, National Oceanic and Atmospheric Administration, 325 Broadway, Boulder, CO 80305-3328 Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309 Department of Chemistry, University of North Texas, P.O. Box 305070, Denton, Texas 762035070 DuPont Central R&D, Wilmington, Delaware 19880, United States

16 17 18 19 20

# Current Address: Utah Division of Air Quality, Salt Lake, UT, USA $ Current Address: Department of Chemistry and Atmospheric Science, Colorado State University, Fort Collins, CO, 80532 USA & Current Address: Synchrogenix, Wilmington, DE, USA

21 22 23

Running Title: The OH + (E)-CF3CH=CHCF3 Reaction

24 25

*Corresponding author: James B. Burkholder

26

e-mail: [email protected]

27

Phone: (303)-497-3252

28 29

1

ACS Paragon Plus Environment

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30

Abstract

31

(E)-CF3CH=CHCF3 ((E)-1,1,14,4,4-hexafluoro-2-butene, HFO-1336mzz(E)) were measured over

32

a range of temperature (211–374 K) and bath gas pressure (20–300 Torr; He, N2) using a pulsed

33

laser photolysis-laser induced fluorescence (PLP–LIF) technique. k1(T) was independent of

34

pressure over this range of conditions with k1(296 K) = (1.31 ± 0.15) × 10-13 cm3 molecule-1 s-1 and

35

k1(T) = (6.94 ± 0.80) × 10-13 exp[-(496 ± 10)/T] cm3 molecule-1 s-1, where the uncertainties are 2s

36

and the pre-exponential term includes estimated systematic error. Rate coefficients for the OD

37

reaction were also determined over a range of temperature (262–374 K) at 100 Torr (He). The OD

38

rate coefficients were ~15% greater than the OH values and showed similar temperature dependent

39

behavior

40

k2(296 K) = (1.53 ± 0.15) × 10-13 cm3 molecule-1 s-1. The rate coefficients for reaction 1 were also

41

measured using a relative rate technique between 296 and 375 K with k1(296 K) measured to be

42

(1.22 ± 0.1) × 10-13 cm3 molecule-1 s-1 in agreement with the PLP-LIF results. In addition, the 296

43

K rate coefficient for the O3 + (E)-CF3CH=CHCF3 reaction was determined to be >[OH],

105

with OH radicals produced via the 248 nm (KrF excimer laser) pulsed laser photolysis of H2O2

106

(hydrogen peroxide) or (CH3)3COOH (t-butyl hydrogen peroxide)

107

H2O2 + hn ® 2OH

(3)

108

(CH3)3COOH + hn ® product + OH

(4)

109

where the OH quantum yield for reaction 3 is 2 6 and unity for reaction 4.11 H2O2 photolysis was

110

used for kinetic measurements at temperatures >250 K. (CH3)3COOH photolysis was used over

111

the temperature range 211 to 298 K. The initial OH radical concentration, [OH]0, was estimated

112

from the precursor concentration, its absorption cross section at 248 nm and the photolysis laser

113

power measured at the exit of the LIF reactor with a calibrated power meter. The photolysis laser

4


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114

fluence was varied between 3 and 17 mJ cm-2 pulse-1 over the course of our study. The

115

concentrations of H2O2 and (CH3)3COOH in the LIF reactor were estimated from the pseudo first-

116

order rate coefficients measured in the absence of (E)-CF3CH=CHCF3, as described later.

117

OD radicals were produced using 248 nm pulsed laser photolysis of O3 ([O3] ~4 × 1012

118

molecule cm-3) in a He bath gas to produce O(1D) followed by its reaction with D2O ([D2O] ~3 ×

119

1016 molecule cm-3) O(1D) + D2O ® 2OD

120

(5)

121

The D2O concentration was sufficient to remove 99% of the O(1D) within 1 µs after the photolysis

122

pulse and quench vibrationally excited OD that was produced.

123

OH radical fluorescence was detected following pulsed laser excitation in the

124

A2Σ+(v = 1) ← X2Π(v = 0) transition near 282 nm using the frequency doubled output from a

125

Nd:YAG pumped dye laser. OD fluorescence was detected following excitation near 287.6 nm.

126

The probe laser beam propagated through the LIF reactor at a right angle to the larger diameter

127

photolysis laser beam. The photolysis and probe beams intersected in the middle of the reactor.

128

Fluorescence from the reaction zone was detected by a photomultiplier tube (PMT) orthogonal to

129

the plane of the photolysis and probe laser beams. A band-pass filter (308 nm, FWHM = 10 nm)

130

mounted in front of the PMT was used to isolate the OH fluorescence in the

131

A2Σ+(v = 0) ® X2Π(v = 0) transition. The PMT signal was averaged for 100 laser shots with a

132

gated charge integrator. OH temporal profiles were measured by varying the delay between the

133

photolysis and the probe lasers (i.e., the reaction time) between 10 µs – 20 ms. Both the photolysis

134

and probe lasers were operated at 10 Hz.

135

OH temporal profiles followed the integrated first-order rate expression: [%&]

,

ln #[%&] ( * = ln #,( * = −(01 [(2 ) − CF6 CH = CHCF6 ] + 09 ): = −0 ; :

136

)

)

(I)

137

where St is the measured OH signal at time t, which is proportional to [OH]t, [(E)-CF3CH=CHCF3]

138

is the (E)-CF3CH=CHCF3 concentration in the LIF reactor, k¢ and kd are the first-order rate

139

coefficients for loss of OH in the presence and absence of the (E)-CF3CH=CHCF3, respectively.

140

k¢ values were obtained from a non-linear least-squares fit of St versus time. kd represents the loss

141

of OH due to its reaction with the OH precursor and diffusion out of the detection volume. kd

142

values depended on the OH radical precursor and its concentration and were in the 50–500 s-1

143

range.

OH temporal profiles were measured over a range of HFO concentrations at each

5



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144

temperature and pressure. Rate coefficients, k1(T), were determined from a linear least-squares fit

145

of k¢ versus [(E)-CF3CH=CHCF3] weighted by the measurement precision. kd values measured in

146

the absence of the reactant and obtained from the eq. I fit agreed to within 5%.

147

2.2. Relative Rate Measurements. In the relative rate (RR) method, the loss of the reactant

148

compound, HFO, was measured relative to the loss of a reference compound that has a well-

149

established rate coefficient. Provided the reactant and reference compounds are lost solely via the

150

OH reaction the rate coefficients for the two reactions are related by:

151

ln #

[(?@ >&A>&>?@ ]) [(?@ >&A>&>?@ ](

* =

BC BDEF

ln #

[GHI]) [GHI](

*

(II)

152

where [(E)-CF3CH=CHCF3]0, [(E)-CF3CH=CHCF3]t, [ref]0, and [ref]t are the initial reactant and

153

reference concentrations at time zero and the concentrations following reaction at the time t. kE and

154

kref are the rate coefficients for the (E)-CF3CH=CHCF3 and reference reaction with OH,

155

respectively.

156

exp(-1020/T) cm3 molecule-1 s-1 for the OH + C2H6 reaction with NASA/JPL defined uncertainty

157

parameters of f(298 K) = 1.07 and g = 50.6 Several experiments were performed using CH3CH2Cl

158

as the reference compound, however, deviations from eqn. II, which we attribute to secondary Cl-

159

atom chemistry, were observed and particularly noticeable at higher extent of reaction.12 Results

160

using CH3CH2Cl as the reference compound were not included in the final analysis.

C2H6 was used as the reference compound where k(T) = 7.66 × 10-12

161

The apparatus used for the relative rate measurements has been described elsewhere.5

162

Basically, the apparatus consists of a 100 cm long reaction cell (5 cm i.d.) coupled to a Fourier

163

transform infrared spectrometer (FTIR) for monitoring the loss of reactants. OH radicals were

164

produced via 248 nm pulsed laser photolysis of O3 in a He bath gas and an excess of H2O (>10

165

Torr) to produce O(1D) followed by its reaction with H2O:

166

O(1D) + H2O ® 2OH

(6)

167

Experiments were performed by first filling the reactor with (E)-CF3CH=CHCF3, C2H6, H2O

168

vapor, and ~100 Torr He bath gas. The gases were thoroughly mixed using a Teflon diaphragm

169

circulation pump and the initial infrared spectrum recorded. Ozone was then slowly added to the

170

circulating gas mixture while the photolysis beam was passed along the length of the reactor. The

171

residence time of the gas in the reaction cell was ~6 s. The steady-state concentration of O3 was

172

estimated to be ~1 × 1014 molecule cm-3.

6


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173

The loss of the reactant and the reference compounds were measured by infrared absorption

174

while the gas mixture was circulated between the reactor and the infrared absorption cell. Infrared

175

spectra were recorded at a spectral resolution of 1 cm-1 between 500 and 4000 cm-1 in 20 co-

176

additions. The loss of C2H6 was determined by monitoring the change in the absorption band near

177

820 cm-1 while the loss of (E)-CF3CH=CHCF3 was monitored using the absorption band near 1320

178

cm-1. Dark experiments performed under conditions identical to those used in the RR experiments,

179

but without the photolysis laser beam, showed no observable change, >[(E)-CF3CH=CHCF3]. Experiments were performed using the same setup used in the

191

relative rate measurements described above. Experiments were also performed using the multi-

192

pass infrared absorption cell as the reactor, i.e., without circulation of the gases.

193

concentration was in the range (1.9–8.6) × 1016 molecule cm-3 and was quantified using its infrared

194

absorption band near 2100 cm-1 (1.36 × 10-18 cm2 molecule-1).13,14 The (E)-CF3CH=CHCF3

195

concentration was in the range (3.9–7.5) × 1014 molecule cm-3 and [O2], when added, was in the

196

range (0.5–10) × 1016 molecule cm-3. Rate coefficients were obtained from a linear least-squares

197

fit of k¢ versus [O3].

measured

under

pseudo-first

order

conditions

in

(E)-CF3CH=CHCF3,

The O3

198

2.4. UV and Infrared Absorption Measurements. UV and infrared absorption cross

199

sections of (E)-CF3CH=CHCF3 were determined in this work for use in monitoring the

200

[(E)-CF3CH=CHCF3] online in the PLP-LIF kinetic measurements and for the determination of

201

their global warming potentials. Absorption cross sections were determined at room temperature,

202

296 K, using absolute pressure measurements under static conditions with manometrically

203

prepared mixtures of (E)-CF3CH=CHCF3 (0.01 and 9% in a He bath gas).

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204

UV (184.9 nm) absorption was measured using a Hg pen-ray lamp light source, a 100 cm long

205

absorption cell, and a 185 nm band-pass filter mounted in front of a solar-blind photodiode

206

detector. Absorption cross sections were determined from measurements made over a range of

207

(E)-CF3CH=CHCF3 concentrations using Beer’s Law: K

A = −ln #K * = σ L [(2 ) − CF6 CH = CHCF6 ]

208

)

(III)

209

where I and I0 are the transmitted intensity through the cell with and without (E)-CF3CH=CHCF3,

210

respectively, s is the (E)-CF3CH=CHCF3 absorption cross section at 184.9 nm, and L is the path

211

length of the cell. A range of (E)-CF3CH=CHCF3 concentrations, (7.35–27.5) × 1016 molecule

212

cm-3, were used. The absorbance, A, obeyed eqn. III and a linear least-squares analysis of A versus

213

[(E)-CF3CH=CHCF3] yielded the absorption cross section of (5.72 ± 0.04) × 10-20 cm2 molecule-1,

214

where the quoted uncertainties are the fit precision. Absorption cross sections obtained using

215

independently prepared sample mixtures were identical to within the precision of the measurement.

216

Infrared absorption spectra were recorded using a FTIR equipped with a low volume

217

multi-pass absorption cell (500 cm3, 485 cm optical path length) and HgCdTe detector. Spectra

218

were measured between 500 and 4000 cm-1 with a spectral resolution of 1 cm-1. During the PLP-

219

LIF kinetic experiments infrared absorption measurements were made either before or after the

220

LIF reactor.

221

absorption measurements was scaled to account for the differences in pressure and temperature

222

between the absorption cells and the LIF reactor to obtain its concentration in the LIF reactor.

The (E)-CF3CH=CHCF3 concentration determined from the UV and infrared

223

2.5. Materials. He (UHP, 99.999 %), N2 (UHP, 99.99%), N2 (UHP, 95%)

225

was prepared by bubbling N2 through a sample that was initially ~60% mole fraction. H2O2 and

226

(CH3)3COOH were introduced into the gas flow by passing a small flow of He through a bubbler

227

containing the liquid samples. H2O2 and (CH3)3COOH were added to the main gas flow just prior

228

to entering the LIF reactor. O3 was stored in a 195 K silica gel trap and swept into the reactor by

229

passing a He bath gas flow through the trap.

230

The (E)-CF3CH=CHCF3 (99.95% purity) sample was degassed in several freeze-pump–thaw

231

cycles

232

(Z)-CF3CH=CHCF3 (0.04 wt%) and HCFC-122 (CHCl2CClF2) (0.01 wt%). Mixtures of the

233

samples in a He bath gas were prepared manometrically in 12 L Pyrex bulbs. Mixing ratios in the

before

use.

Quoted

sample

impurities

8

for


(E)-CF3CH=CHCF3

included

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234

range 10–35% were used during the course of the experiments. The bulb content was monitored

235

using infrared absorption and found to be stable to within ~1% over the duration of our study.

236

Gas flows were measured with calibrated mass flow meters and pressures were measured

237

using capacitance manometers. The gas flow velocity in the PLP-LIF experiments was in the

238

range 6–20 cm s-1 ensuring a fresh sample of gas in the LIF reaction volume for each photolysis

239

pulse. Uncertainties quoted herein are 2s unless noted otherwise.

240

3. Results and Discussion

241

3.1 OH reaction rate coefficients obtained using PLP–LIF. Rate coefficients for reaction 1

242

were measured over the temperature range 211–374 K at pressures between 20 and 300 Torr (He,

243

N2). A summary of the experimental conditions and the rate coefficients obtained is given in Table

244

1.

245

measurements at all temperatures included in this study. Representative measured OH decay

246

profiles are provided in Figure S1 of the Supporting Information. The OH decay profiles followed

247

pseudo first-order kinetics, i.e., single exponential decays, under all experimental conditions.

The reaction was found to be independent of pressure to within the precision of the

248 249 250

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251 252

Page 10 of 39

Table 1. Summary of experimental conditions and rate coefficients obtained in this work for the OH + (E)-CF3CH=CHCF3 reaction, k1(T) T (K)

P (Torr)

Bath Gas

v (cm s-1)

Laser fluence (mJ cm-2 pulse-1)

He He

[O2] (10 molecule cm-3) – 4.50

211 211

200 200

6.1 6.1

219 219 220

200 200 200

He He N2

– 4.37 –

240 240

200 200

He He

253 252 252

100 100 100

270 296 296 296 296 296 296 297 296 296

[(E)-CF3CH=CHCF3] (1015 molecule cm-3)

8.0 8.0

[OH]0 (10 molecule cm-3) 0.12a 0.12a

6.2 6.2 6.6

8.1 8.1 7.6

1.05 0.75 0.62

0.21a 0.15a 0.12a

1.59-22.2 2.50-28.8 2.60-19.0

– 4.15

6.5 6.5

6.54 6.54

1.24 1.24

0.20a 0.20a

1.88-48.0 1.21-36.9

He N2 N2

– – 4.65

6.8 6.3 6.3

9.7 8.0 8.0

0.47 0.59 0.59

1.86b 1.90b 1.90b

1.60-95.4 0.95-65.7 1.30-68.0

100

He

–

7.1

8.8

0.49

1.60b

2.92-70.4

20

He

–

20.6

4.0

1.43

2.56b

1.02-38.0

1.25

b

0.98-67.0

1.31 ± 0.02

b

9.00-74.2

1.31 ± 0.02

b

0.65-47.0

1.29 ± 0.01

a

4.09-40.8

1.29 ± 0.01

b

3.43-40.4

1.29 ± 0.03

b

1.49-47.6

1.32 ± 0.02

b

2.20-71.0

1.31 ± 0.02

b

0.17-2.10

1.34 ± 0.03

52 54 100 200 300 25 200 200

He He He He He N2 N2 N2

– 3.4 – – – – – 4.39

8.6 8.4 10 8.1 7.8 6.7 7.4 7.4

4.8 4.8

1.25

9.7

0.45

6.5

1.54

5.3

0.31

5.5

0.45

5.5

0.46

5.5

0.46

11

2.00 2.00 1.76

0.25 0.66 0.57 0.57 0.57

2.54-28.8 2.21-29.0

k1 -13

c

[precursor] (1014 molecule cm-3) 0.60 0.60

16

(10 cm3 molecule-1 s-1) 0.679 ± 0.01 0.673 ± 0.01 k1(211 K) = 0.668 ± 0.01d 0.741 ± 0.01 0.730 ± 0.01 0.725 ± 0.02 k1(220 K) = 0.726 ± 0.01d 0.877 ± 0.01 0.878 ± 0.01 k1(240 K) = 0.879 ± 0.01d 0.940 ± 0.01 0.962 ± 0.01 0.966 ± 0.01 k1(252 K) = 0.962 ± 0.01d 1.11 ± 0.01 k1(270 K) = 1.11 ± 0.01d 1.32 ± 0.02

k1(296 K) = 1.31 ± 0.01d 319 341

100 100

He He

– –

7.7 7

15.9 3.8

0.49 0.55

10


1.77b 0.48b

2.33-55.5 1.44-51.0

1.47 ± 0.01 1.60 ± 0.06

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253 254 255 256


357

100

He

–

7.9

15.9

0.52

1.87b

1.80-45.3

374 374 374

100 100 100

He N2 N2

– 3.76 –

10 9.8 9.8

4.4 14.3 14.3

0.65 0.43 0.43

0.65b 1.29b 1.29b

0.81-48.8 0.80-46.0 0.80-46.0

a

1.73 ± 0.02 1.82 ± 0.05 1.88 ± 0.04 1.84 ± 0.05 k1(373 K) = 1.84 ± 0.03d

t-C4H9OOH was used as the OH precursor. b H2O2 was used as the OH source. c The quoted uncertainties are the 2s precision from the linear least-squares fit of k¢ versus [(E)-CF3CH=CHCF3]. d Determined from a weighted linear least-squares fit to all (k¢- kd) versus [(E)-CF3CH=CHCF3].

257

11



258

Figure 1 shows the second-order plots for reaction 1 obtained at 296 K and the temperature

259

extremes, 211 and 374 K, included in this study. The obtained (k¢ - kd) values varied linearly with

260

the (E)-CF3CH=CHCF3 concentration over the entire range of concentrations employed and with

261

changes in various experimental parameters such as [OH]0, photolysis laser fluence, OH radical

262

precursor, and linear gas flow velocity as outlined in Table 1. The measured rate coefficients were

263

independent of O2 addition to the reaction mixture. In the final analysis, k1(T) was obtained from

264

a weighted linear least-squares fit, eq. I, including all data obtained at a given temperature. The

265

fits shown in Figure 1 reproduce the experimental data very well with k1(296 K) =

266

(1.31 ± 0.01) × 10-13 cm3 molecule-1 s-1, where the quoted uncertainty is the linear least-squares fit

267

precision.

268

269 270 271 272 273 274

Figure 1. Pseudo-first-order rate coefficient data for the reaction of OH with (E)-CF3CH=CHCF3 obtained in this work at 296 K and the temperature extremes included in this study. Error bars on the individual data points are suppressed for clarity. The precision in (k¢ - kd) is 100 s-1, or less, and the absolute uncertainty in [(E)-CF3CH=CHCF3] is ~5% (see text). The lines are linear least– square fits of the data to eq. I. A summary of the experimental results is given in Table 1.

275 276

Figure 2 shows the temperature dependence of the measured rate coefficients for reaction 1.

277

k1(T) has a positive temperature dependence over the entire temperature range, 211–374 K, that is

12


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278

described by the Arrhenius expression k1(T) = (6.94 ± 0.24) × 10-13 exp[-(496 ± 10)/T] cm3

279

molecule-1 s-1, where the quoted uncertainties are the fit precision.

280

281 282 283 284 285 286 287 288 289

Figure 2. Rate coefficient temperature dependence for the OH (filled circles and triangles) and OD (open circles) reaction with (E)-CF3CH=CHCF3 measured in this work using the pulsed laser photolysis–laser induced fluorescence (PLP-LIF) and relative rate (RR) (green squares) techniques. The different colored symbols represent experiments performed in He (blue), N2 (red), and with O2 added (solid triangles). The solid and dashed lines are least-squares Arrhenius expression fits to the data. The gray shaded region represents the estimated range of absolute uncertainty for reaction 1. The Arrhenius expression for the OH + (Z)-CF3CH=CHCF3 reaction taken from Baasandorj et al.2 is included for comparison (dotted line).

290 291

In a relative rate study, Østerstrom et al.9 reported k1(296 K) to be (1.72 ± 0.42) × 10-13 cm3

292

molecule-1 s-1, which is ~30% greater than the present PLP-LIF and RR results. Their value does,

293

however, agree with our value within the combined uncertainties of the two studies.

294

3.1.1. OD + (E)-CF3CF=CHF. The OD + (E)-CF3CH=CHCF3 reaction rate coefficients, k2(T),

295

were measured over the temperature range 262–374 K. A summary of the experimental conditions

296

and rate coefficients obtained in these experiments is given in Table 2. The OD temporal profiles

13



Page 14 of 39

297

followed pseudo-first-order kinetics under all experimental conditions.

Combining all the

298

measurements obtained at 296 K yielded k2(296 K) = (1.53 ± 0.02) × 10-13 cm3 molecule-1 s-1

299

where the uncertainty is the fit precision. k2(T) is systematically about 15% greater than the rate

300

coefficients obtained for the OH reaction, which implies that the reaction mechanism is

301

predominately controlled by radical addition to the double bond. Note that the modest increase in

302

OD reactivity is similar to that reported for the OH/OD reactions with the HFOs CH2=CHF and

303

CH2=CF2 reported from our laboratory.15

304

The temperature dependence of the rate coefficient for reaction 2 is similar to that of reaction

305

1 with k2(T) = (7.52 ± 0.44) ´ 10-13 exp[-(476 ± 20)/T] cm3 molecule-1 s-1 where the quoted

306

uncertainties are from the precision of the fit. The rate coefficient data for reaction 2 is included

307

in Figure 2 for comparison with the rate coefficients obtained for the OH reactions.

308

Østerstrom et al.9 reported k2(296 K) as part of their relative rate study. Their value of 5.61

309

´ 10-13 cm3 molecule-1 s-1 is a factor of 3.7 greater than that obtained in the present study. Their

310

reported k2(296 K)/k1(296 K) ratio is 3.3, which is in poor agreement with our measured ratio of

311

1.17. On the basis of theoretical calculations, Østerstrom et al.9 interpreted the significantly

312

enhanced OD reactivity to a reduced barrier height for the OD reaction. It is worth noting that the

313

Østerstrom et al.9 study also included OH and OD radical relative rate measurements for the

314

(Z)-CF3CH=CHCF3 stereoisomer. In this case, they report a k2(296 K)/k1(296 K) ratio of 1.65,

315

which is greater, but much closer to the value reported in Baasandorj et al.2 from our laboratory,

316

1.17, which was based on absolute PLP-LIF measurements. The source of the discrepancy in the

317

OD rate coefficient results between the present work and Østerstrom et al.9 is presently unclear.

318

14


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319

Table 2. Summary of experimental conditions and rate coefficients obtained in this work for the OD + (E)-CF3CH=CHCF3

320

reaction

321 322 323

T (K)

P (Torr, He)

v (cm s-1)

Photolysis Laser fluence (mJ cm-2 pulse-1)

[O3] (10 molecule cm-3)

[D2O]/[O2] (1016 molecule cm-3)

[OH]0 (10 molecule cm-3)

262 262

100 100

8.52 8.52

8.1 8.1

4.0 4.0

3.26/– 3.26/3.28

9.8 9.8

296 296

100 100

9.3 9.5

9.4 9.4

3.7 3.6

3.03/– 3.03/2.9

9.5 9.2

339 339

100 100

9.5 9.5

9.4 9.4

3.25 3.25

2.79/– 2.79/2.67

8.4 8.4

374 374

100 100

11.4 11.4

6.5 6.5

3.0 3.0

2.48/– 2.48/–

5.4 5.4

12

11

a

[(E)-CF3CH=C ka -13 HCF3] (10 cm3 15 (10 molecule molecule-1 s-1) -3 cm ) 1.99-35.9 1.26 ± 0.02 1.94-31.8 1.25 ± 0.01 k(262 K) = 1.25 ± 0.01b 1.70-30.8 1.53 ± 0.02 1.37-2.8 1.53 ± 0.03 k(296 K) = 1.53 ± 0.02b 1.27-22.8 1.84 ± 0.02 1.33-22.6 1.83 ± 0.02 k(339 K) = 1.84 ± 0.01b 1.00-22.3 2.14 ± 0.02 1.20-20.7 2.12 ± 0.02 k(374 K) = 2.13 ± 0.02b

The quoted uncertainties are 2s of the measurement precision. b Determined from a weighted linear least-squares fit to all (k¢- kd) versus [(E)-CF3CH=CHCF3].

15



Page 16 of 39

324

3.2. Relative Rate (RR) Measurements. Figure 3 shows the results obtained in the relative

325

rate coefficient measurements for reaction 1 at 296, 315, 340, 348, and 375 K. The results are

326

given in Table 3 and included in Figure 2 for comparison with the absolute PLP-LIF measurement

327

results.

328

measurements, with the PLP-LIF results over the entire temperature range.

329 330

Table 3. Summary of OH + (E)-CF3CH=CHCF3 relative rate results a

331 332 333

334 335 336 337 338 339 340 341 342

a

The RR results are in agreement, to within the combined uncertainties of the

Temperature (K) 296 315 340 348 375

Experiments

kE/kref b

4 1 2 1 3

0.500 ± 0.04 0.480 ± 0.04 0.404 ± 0.03 0.413 ± 0.03 0.354 ± 0.03

k1 (10-13 cm3 molecule-1 s-1) 1.22 ± 0.10 1.44 ± 0.11 1.54 ± 0.12 1.69 ± 0.14 1.77 ± 0.14

C2H6 reference compound, kref(T) = 7.66 × 10-12 exp(-1020/T) cm3 molecule-1 s-1 for OH + CH3CH3;6 b Value obtained from fit of all data at the given temperature.

Figure 3. Relative rate data for the OH + (E)-CF3CH=CHCF3 reaction obtained in this work at 296 K (circles), 315 K (dashed red line, closely overlaps the fit of the 296 K data), 340 K (dashed green line), 348 K (dashed blue line), and 375 K (triangles). The data points obtained at 315 K, 340 K, and 348 K are omitted for clarity, while the range of the dashed line represents the range of the experimental data. Error bars on the individual data points are suppressed for clarity, but are approximately ±0.01 for both the CF3CH=CHCF3 and C2H6 measurement precision. The lines are linear least-squares fits to all the data obtained at each temperature, Table 3.

16


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343 344 345 346

3.3.

O3 Reaction Rate Coefficient.

Rate coefficients for the reaction of O3 with

(E)-CF3CH=CHCF3: O3 + (E)-CF3CH=CHCF3

® Products

(7)

347

were measured at 296 K. The experimental data are plotted in Figure S2 of the supporting

348

information. The decay of the HFO in the presence of excess O3 followed pseudo first-order

349

kinetics and there was no observable change,

Rate Coefficient Measurements and Theoretical ... - ACS Publications

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