2
08
L. Chen et al. / Chemical Physics Letters 514 (2011) 207–213
temperature range of 253–328 K by means of two thermocouples,
one attached to each side of the reaction chamber.
correcting for the nonreactive decay (0.2%) due to removal of
the sample and reference compound for each GC-FID analysis
Hydroxyl radicals were produced by UV photolysis of O
3
, which
n
(D = n ln 0.998, where n is the sampling number of the GC-FID
was generated from pure O (99.5% pure; Nihon Sanso Corp., Japan)
2
analysis [10]).
with a silent-discharge ozone generator (ECEA-1000, Ebara Jitsu-
gyo Co., Japan) in the presence of water vapor at an initial He pres-
sure of 200 Torr (99.995% pure; Iwatani International Corp., Osaka,
Japan) [10]:
For determination of k
(98.5% pure) and pure i-C
from the HFE-7100 sample with a gas chromatograph equipped
with a stainless steel column (9.6 mm i.d., 1.2 m long) packed
with KRYTOX 143AC. The apparatus and procedure for the
3
and k , samples of pure n-C
4
4 9 3
F OCH
4
F
9
OCH (99.99% pure) were purified
3
1
O
3
þ h
m
! Oð DÞ þ O
2
ð5Þ
ð6Þ
4 9 3 4 9 3
purification of n-C F OCH and i-C F OCH have been described
in detail previously [11]. The typical initial concentrations (in
1
–3
15
17
Oð DÞ þ H
2
O ! 2OH
molecules cm ) were 1.0 ꢀ 10 (n/i-C F OCH ) and 5.6 ꢀ 10
4
9
3
(
H
2
O) in He at 200 Torr. The decay of the reactant was ꢃ75% over
a 100-min irradiation period at 298 K. The loss of n/i-C OCH
and the formation of n/i-C OC(O)H and other products were
monitored with an FT-IR spectrometer (JIR-6500, JEOL, Japan)
with nickel-coated aluminum multiple-reflection IR cell
(375 cm ; optical path length 3 m) at a resolution of 0.5 cm
Ten 40-W low-pressure Hg lamps (254 ± 8 nm) surrounding the
reaction chamber were used as the UV light sources for the deter-
4
F
9
3
4 9
F
mination of k
ment of the products of the reactions of n/i-C
radicals and rate constants k and k . An O /O (3%, O
3
was continuously introduced at a flow rate of 1–2 cm min at
STP into the reaction chamber during the UV irradiation period.
A greaseless vacuum line was used for preparation of the reaction
gas mixtures.
1
and k
2
; and two lamps were used for the measure-
OCH with OH
) gas mixture
4
F
9
3
a
3
4
3
2
3
–1
3
ꢁ1
.
The sample in the reaction chamber was continuously circulated
through the IR cell by a magnetically driven glass circulating
pump at a flow rate of 850 cm min
3
ꢁ1
during UV irradiation.
OCH , CF CF CF C(O)F,
were quantified from the IR
The concentrations of n-C
4
F
9
OCH
3
, i-C
4
F
9
3
3
2
2
For the determination of k
were each analyzed relative to a reference compound, CF
CF CF OCH . CF OCH (99% pure) and CF CF OCH
obtained from Research Institute of Innovative Technology for the
Earth (Kyoto, Japan). Because n-C OCH and i-C OCH were
used as a mixture, the data for k and k were simultaneously mea-
sured in a single experiment. The initial concentrations (molecules
1
and k
2
, n-C
F
4 9
OCH
3
and i-C
4
F
9
OCH
3
(
CF CFC(O)F, CF C(O)F, and COF
3
)
2
3
2
3
OCH
3
or
–1
absorptions at 1460, 1460, 1888, 1889, 1902, and 1928 cm
respectively, of their He mixtures of known concentration at a
total pressure of 200 Torr at 298 K. CF CF CF C(O)F (99% pure),
CF CFC(O)F (99% pure), and CF C(O)F (99% pure) were obtained
,
3
2
3
3
3
3
2
3
(99% pure) were
3
2
2
4
F
9
3
4
F
9
3
(
3
)
2
3
1
2
from Asahi Glass Co. (Japan), and COF
from SynQuest (Alachua, FL, USA).
2
(95% pure) was purchased
–
3
14
14
cm
)
were 4.7 ꢀ 10
(n-C
.0 ꢀ 10 (reference compound), and (0.36–5.8) ꢀ 10 (H
00 Torr of He. The absolute concentrations of n-C OCH
OCH , and the reference compounds were determined with a
4
F
9
OCH
3
), 8.3 ꢀ 10
(i-C
4
F
9
OCH
O) in
, i-
3
),
15
17
n-C
and a precursor for n-C
only react with OH radicals but also undergo photolysis under
UV irradiation. Therefore, n-C OC(O)H and i-C OC(O)H are
the intermediates in the following consecutive reactions:
4
F
9
OCH
3
or i-C
4
F
9
OCH
3
served as both a reference compound
1
2
C
2
4
F
9
4 9
OC(O)H and i-C F OC(O)H, which not
4
F
9
3
4
F
9
3
4
F
9
4 9
F
gas chromatograph (GC) with a flame ionization detector (FID)
GC-14A-FID; Shimadzu, Tokyo, Japan) equipped with a stainless
steel column (3 mm i.d., 1 m long) packed with KRYTOX 143AC
GL Sciences Inc., Tokyo Japan). The column oven was set at a con-
stant temperature of 393 K for the measurements of k and k . A
(
n=i-C
n=i-C
n=i-C
4
4
4
F
9
F
9
F
9
OCH
3
þ OH !
OCðOÞH þ OH ! products ðk
OCðOÞH þ h ð254 nmÞ ! products ðJ ; J Þ
a
n=i-C
4
F
9
OCðOÞH þ other products
ð8Þ
ð9Þ
(
1
2
; k
Þ
3
4
3
sample of the gas mixture (0.5 cm ) was extracted from the cham-
ber and transferred to the GC-FID by an automatic sampling sys-
tem at 6-min intervals. In each sampling cycle, the gas mixture
residing in the line between the sampling loop and the chamber
was withdrawn and discarded, and then the gas mixture was
charged into the sampling loop and transferred to the GC-FID.
The mass of reactants decreased by 0.2% with each GC-FID analysis.
The uncertainties in the measured concentrations of reactants
m
ð10Þ
3
4
The parameter
tion of n/i-C OCH
can be determined from Eq. (II) [5]:
a
is the yield of n/i-C
4 9
F OC(O)H from the reac-
4
F
9
3
with OH radicals (
a
= 0–1). The values of
a
3 4
and k and k
n
ꢄ
ꢅ
o
k
J
iþ2
iþ2
a
1þ
ꢁ1
ki
kiþ2½OHꢂav
y ¼
h
i ð1 ꢁ xÞ½ð1 ꢁ xÞ
ꢁ 1ꢂ
k
k
iþ2
i
J
iþ2
were <2% for n-C
4
F
9 3
OCH , i-C
4
F
9
OCH
3
, CF
3
OCH
3
3
, and CF CF
2 3
OCH .
1 ꢁ
ð1 þ kiþ2
Þ
½OHꢂ
av
The reactant percent decays after 90 min of irradiation at 298 K
were 70–80%.
ði ¼ 1; 2Þ
ðIIÞ
The values of k
pearance rate of the sample relative to that of the reference com-
pound in the presence of OH radicals (k ):
1 2
and k were obtained by measuring the disap-
D
½n=i ꢁ C
4
F
9
OCH
3
ꢂt
x ¼
½
n=i ꢁ C
4
F
9
OCH
3
ꢂ0
r
Reference þ OH ! products
Taking into account the nonreactive decay (0.2%) due to re-
moval of the sample and reference compound for each GC-FID
k
r
ð7Þ
½
n=i ꢁ C
4
F
9
OCðOÞHꢂ
t
y ¼
½n=i ꢁ C
4
F
9
OCH
3
ꢂ
0
where J
3
and J
OC(O)H (J
4
are the rates of photolysis of n-C F OC(O)H and
4 9
analysis, we used Eq. (I) to evaluate k
1
/k
r
2 r
and k /k [10]:
–5
i-C
4
F
9
3
and J were determined to be (1.76 ± 0.04) ꢀ 10
4
ꢀ½
Sampleꢂ
ꢁ
k
ꢂ
ꢀ
½Referenceꢂ
½Referenceꢂ
ꢁ
ꢃ
–
5 –1
and (1.88 ± 0.10) ꢀ 10
s , respectively, for two 40 W lamps using
0
i
0
ln
þ D
n
¼ k ln
þ D
n
k
i
ði ¼ 1 or 2Þ
ðIÞ
½
Sampleꢂ
r
the same method reported in our previously study [5,6]); [OH]av is
the average concentration of OH radicals in the reaction chamber;
t
t
and
respectively, the concentration of n/i-C
concentration of n/i-C OC(O)H at reaction time t, and the initial
concentration of n/i-C OCH . However, Eq. (II) is based on the pre-
D
[n/i-C
4
F
9 3
OCH ]
t
, [n/i-C
4
F
9
OC(O)H]
t
, and [n/i-C
4 9 3 0
F OCH ] are,
where [Sample]
trations of the sample (n-C
reference compound (CF OCH
Reference] represent the concentrations of the sample and the
reference compound at reaction time t; and D is a parameter
0
and [Reference]
OCH
or CF
0
represent the initial concen-
and i-C OCH ) and the
CF OCH ); [Sample] and
4
F
9
OCH consumed, the
3
4
F
9
3
4
F
9
3
4 9
F
3
3
3
2
3
t
4
F
9
3
[
t
supposition that the concentration of OH radicals is approximately
constant during measurement [5]. In this study, a nearly constant
n