Product distributions from the OH radical-induced oxidation of n-Pentane and isopentane (2-Methylbutane) in Air

Article abstract of DOI:10.1002/kin.20200

Hydroxyl radicals, generated by photolysis of H₂O₂. were reacted with n-pentane and isopentane in air in the absence of nitrogen oxides. The observed product distributions were compared with similar data derived by computer simulations, based on the known reaction mechanisms, to determine relative probabilities for hydrogen abstraction at different sites of the parent compounds and to estimate branching ratios and relative rate coefficients for cross-combination reactions between different peroxy radicals. For n-pentane. the distribution of the pentanols indicates probabilities for hydrogen abstraction, in percent, of q₁= 9.1 ± 0.7. q ₂ = 56.1 ± 1.8, and q₃ = 34.8 ± 1.3. which agree with predictions based on the algorithm proposed by Atkinson. Branching ratios needed to harmonize calculated and observed product distributions are somewhat larger than, although still within the error ranges of. the values found by us previously Comparison between experimental and calculated data confirms the isomerization and decomposition constants recently established for the three pentoxyl radical isomers. The product distribution for isopentane. which is dominated by acetone, acetaldehyde. 2-methyl-butan-2-ol. and 2-methyl-butan-2-hydroperoxide, is in harmony with the predicted oxidation mechanism. Probabilities for hydrogen abstraction from isopentane were estimated to occur to 12% at the primary. 28% at the secondary, and 60% at the tertiary sites, again in agreement with predictions based on the algorithm of Atkinson.

Full text of DOI:10.1002/kin.20200

Product Distributions from
the OH Radical-Induced
Oxidation of n-Pentane
and Isopentane
(2-Methylbutane) in Air
GERALD HEIMANN, PETER WARNECK
¨
Max-Planck-Institut fur Chemie, 55020 Mainz, Germany
Received 18 October 2005; revised 5 May 2006; accepted 13 May 2006
DOI 10.1002/kin.20200
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Hydroxyl radicals, generated by photolysis of H2O2, were reacted with n-pentane
and isopentane in air in the absence of nitrogen oxides. The observed product distributions
were compared with similar data derived by computer simulations, based on the known reac-
tion mechanisms, to determine relative probabilities for hydrogen abstraction at different sites
of the parent compounds and to estimate branching ratios and relative rate coefficients for
cross-combination reactions between different peroxy radicals. For n-pentane, the distribution
of the pentanols indicates probabilities for hydrogen abstraction, in percent, of q1 = 9.1 0.7,
q2 = 56.1 1.8, and q3 = 34.8 1.3, which agree with predictions based on the algorithm pro-
posed by Atkinson. Branching ratios needed to harmonize calculated and observed product dis-
tributions are somewhat larger than, although still within the error ranges of, the values found
by us previously. Comparison between experimental and calculated data confirms the isomer-
ization and decomposition constants recently established for the three pentoxyl radical iso-
mers. The product distribution for isopentane, which is dominated by acetone, acetaldehyde,
2-methyl-butan-2-ol, and 2-methyl-butan-2-hydroperoxide, is in harmony with the predicted
oxidation mechanism. Probabilities for hydrogen abstraction from isopentane were estimated
to occur to 12% at the primary, 28% at the secondary, and 60% at the tertiary sites, again in
agreement with predictions based on the algorithm of Atkinson. ꢀ 2006 Wiley Periodicals, Inc.
C
Int J Chem Kinet 38: 677–688, 2006
Correspondence to: Peter Warneck; e-mail: Peter.Warneck@
gmx.de.
Contract grant sponsor: German Federal Ministry for Research
and Technology.
c
ꢀ
2006 Wiley Periodicals, Inc.

678
HEIMANN AND WARNECK
of hydrogen abstraction at the different reaction sites
and on the branching ratios of some cross-combination
reactions compared to the self-reactions of peroxy
radicals.
INTRODUCTION
Pentanes are components of automotive fuels that enter
the atmosphere by fuel evaporation and with the engine
exhaust gases. As for other alkanes, the dominant loss
process in the troposphere is reaction with the hydroxyl
radical. This initiates an oxidation process leading to
aldehydes and ketones, with alkylperoxyl and alkoxyl
radicals acting as intermediates [1–3]. The detailed re-
action pathways are of interest not only to atmospheric
chemistry but also to a better understanding of low-
temperature oxidation of alkanes in general. Reaction
mechanisms for the pentanes have remained somewhat
speculative, because hydrogen abstraction may occur
at different sites of the molecule and the subsequent
addition of O2 generates several isomeric pentylper-
oxyl radicals, three in the case of n-pentane and four
in the case of isopentane. Probabilities for their for-
mation can be estimated using formulas developed by
Greiner [4] and Atkinson [5,6] for the abstraction of
a primary, secondary, or tertiary hydrogen atom from
the alkane. In urban and suburban atmospheres, where
nitrogen oxides are abundant, pentylperoxyl radicals
are largely converted to pentoxyl radicals by react-
ing with NO. Pentoxyl radicals, in turn, react partly
with oxygen to form carbonyl compounds, and they
undergo isomerization and/or decomposition, thereby
generating new alkylperoxyl radicals. Although these
processes have received much attention, the rate coeffi-
cients associated with reactions of n-pentoxyl isomers
have been determined with some reliability only re-
cently, experimentally [7–10] as well as theoretically
[11–14]. In the absence of NO, the pentylperoxyl rad-
icals react with each other and with other alkylperoxyl
radicals generated in the system; one branch of each
reaction leads again to pentoxyl radicals, the other to
alcohols and carbonyl compounds. Table I summarizes
the principal reactions occurring in the oxidation of
n-pentane.
We have previously studied the reaction se-
quences following the self-reactions of individual n-
pentylperoxyl radicals formed by photolysis of the cor-
responding iodopentanes [9]. Here, we present results
for the OH-induced oxidation of n-pentane, carried
out under similar NOx -free conditions. The system in-
volves the mutual interactions of the 7 peroxyl radicals
characterized in Fig. 1. In addition, we have explored
the oxidation of isopentane and present our results be-
low. An effort was made to determine the full product
spectrum in each case. This has not been attempted pre-
viously, to our knowledge. Computer simulations were
carried out to assist in the data analysis; for n-pentane,
the previous data were utilized as far as possible. Prod-
uct distributions provide information on the probability
EXPERIMENTAL TECHNIQUES
Apparatus and experimental procedures were similar
to those described previously [15]. The reactions were
carried out in 2-L spherical glass bulbs. Hydroxyl radi-
calsweregeneratedbyphotolysisofhydrogenperoxide
using 254 nm radiation derived from an ozone-free
penray mercury lamp, which was placed into a quartz
finger reaching into the center of the bulb. The lamp
was cooled by a flow of compressed nitrogen. The
bulbs were fitted with Teflon-stoppered shutoff valves
and joints for connection to a gas-handling manifold.
Reaction mixtures consisted of approximately 120 ppm
H2O2 and 0.1% hydrocarbon (mole fraction) in syn-
thetic air at a pressure slightly above atmospheric.
The H2O2 mixing ratio was determined by the va-
por pressure above a concentrated aqueous solution
of H2O2 kept in an ice bath. The actual mixing ra-
tio depended on the extent of equilibration, so that it
was sometimes lower than 120 ppm. In some experi-
ments, when a higher product yield was desirable, the
ice bath was removed to allow the vapor pressure to
rise. The estimated range of H2O2 mixing ratios was
70–350 ppm.
Product concentrations were determined by gas
chromatography with flame ionization detectors. Sam-
ples of the reaction mixtures were transferred to the gas
chromatograph via thin Teflon tubes pushed through a
hole pierced in a septum attached to the reaction ves-
sel. Two septa and transfer lines were needed when
the analysis required the simultaneous application of
two GC systems. Inlet lines and sampling loops of the
gas chromatographs were made of quartz-lined stain-
less steel tubes. The sampling valve was kept at a tem-
perature of 80◦C. Two capillary columns (50 m long,
0.32 mm i.d.) were required to separate the products:
a CPSil 76 column, coated with dimethylpolysiloxane
(0.34 ꢀm film thickness); and a CP-Wax 57 CB col-
umn, coated with polyethylene glycol (0.23 ꢀm film
thickness). The nitrogen carrier flow rate was 3 cm3
min−1 for both. The temperature programs also were
similar: 30◦C isothermal for 3 min, heating to 65◦C
at a rate of 8◦C min−1, followed by further heating to
200◦C at a rate of 30◦C min−1, and finally constant for
3 min at 200◦C. In some experiments, the CP-Wax 57
column was replaced by a CP-Wax 52 column with the
following temperature program: 40◦C isothermal for 2
min, heating to 160◦C at a rate of 20◦C min−1, followed
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PRODUCT DISTRIBUTIONS FROM THE OH RADICAL-INDUCED OXIDATION
679
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680
HEIMANN AND WARNECK
Figure 1 Peroxyl radicals occurring in the oxidation of n-pentane and their identification by numbers. The numbers are used
as subscripts of rate coefficients and branching ratios associated with mutual reactions.
by further heating to 210◦C at a rate of 30◦C min−1
,
present study was not focused on isomerization prod-
ucts, and no attempts were made to identify them.
and finally constant for 3 min at 210◦C. Products were
identified by comparison of retention times with au-
thentic samples of alcohols, aldehydes, and ketones.
Calibration curves for peak area versus concentration
of individual compounds were obtained with samples
prepared by successive dilution of mixtures containing
known amounts of the pure substance in air. Daily cali-
bration checks were then carried out with suitable mix-
tures of substances in air that covered the concentration
range encountered. Most of the substances were avail-
able commercially with a purity of at least 99.9%. In
the oxidation of n-pentane, the CPSil column showed
a product eluting after 9.9 min retention time, about
3 min later than the main group of alcohols and car-
bonyl compounds. Because this is typical of a bifunc-
tional compound, the additional peak was assigned to
be an isomerization product. In this case, 4-hydroxy-
3-methyl-butan-2-one was used as a surrogate for cal-
ibration because its retention time was close to that
of the unknown product. Subsequent to completing the
bulk of the experiments, one of the expected isomeriza-
tion products, 1-hydroxy-pentan-4-one, became com-
mercially available. Both compounds were compared
on the CP-Wax 52 column. Their response was similar
but the latter eluted much later than the former. The
MODEL CALCULATIONS
The FACSIMILE computer code [16] was employed
to calculate the rise of product concentrations with
time and the ensuing product distributions. Calcula-
tions were based on comprehensive chemical mech-
anisms that took into account the interactions of all
peroxy radicals in the system as well as reactions of
the alkoxyl radicals. These reactions were added to
the basic reactions involving H2O2 and HO2 radicals.
Rate coefficients applied for the reactions of OH rad-
icals with n-pentane and isopentane are 4.0 × 10−12
and 3.7 × 10−12 cm3 molecule−1 s−1, respectively [1].
More recent values presented by Atkinson and Arey
[2] are slightly lower: 3.8 × 10−12 and 3.6 × 10−12 cm3
molecule−1 s−1, but using these data would have no ef-
fect on the relative product distributions. Relative prob-
abilities for hydrogen abstraction at different sites of
the two alkanes were initially estimated from the ex-
perimental data and subsequently refined by the calcu-
lations. Table I shows the principal reactions occurring
during the oxidation of n-pentane, Table II summarizes
Table II Known Rate Coefficients and Branching Ratios (at 298 K) Involved in n-Pentane Oxidation
k(OH + n-pentane) = 4.0 × 10−12 cm3 molecule−1 s−1 [1]
α11 = 0.42 0.17, α22 = 0.46 0.10, α33 = 0.40 0.08 [9]
k44 = 3.0 × 10−13 cm3 molecule−1 s−1 [1,17]
k55 = (6.6 0.2) × 10−14 cm3 molecule−1
s
−1, α55 = 0.63 0.06 [1,17]
1kisom = (4.0 1.1) × 105 s−1 [9], 2.0 × 106 s−1 [12], 2.2 × 106 s−1 [14]
2kisom = 2.5 × 105 s−1 [7,11], (1.0 0.2) × 105 s−1 [9], 5.0 × 105 s−1 [12], 3.3 × 105 s−1 [14]
2kdec = 9.1 × 103 s−1 [7,11], (8.4 1.7) × 103 s−1 [9], 1.0 × 104 s−1 [12], 2.2 × 104 s−1 [13]
3kdec = 2.6 × 104 s−1 [8,11], (2.6 0.3) × 104 s−1 [9], (3.3 0.65) × 104 s−1 [10], 3.3 × 104 s−1 [12], 3.4 × 104 s−1 [13]
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PRODUCT DISTRIBUTIONS FROM THE OH RADICAL-INDUCED OXIDATION
681
known values of rate coefficients and branching ratios
RESULTS
for this system, and Fig. 1 shows structures of the per-
oxyl radicals involved in the oxidation of n-pentane and
the number code used to identify their interactions by
suffixes of rate coefficients and branching ratios. Major
uncertainties exist for the rate coefficients of peroxyl
radicals, mainly C5 alkyl peroxyl and hydroxy-alkyl
peroxyl radicals, because most of them have not been
measured. Accordingly, we had to work with estimates.
As previously [9,15], we have differentiated between
primary, secondary, and tertiary alkylperoxyl radicals
n-Pentane
The following products were detected and quantified:
ethanal, propanal, pentanal, and the two isomeric pen-
tanones, the three pentanols, and one or more unspec-
ified isomerization products, occurring on the CPSil
column at a retention time typical of a C5 hydroxy-
carbonyl compound. Small amounts of ethanol and
propan-1-ol were also detected. Butanal, which was ob-
served in the photo-oxidation of 1-iodopentane, could
not be unambiguously identified. Two GC columns
were required to separate the products. The CPSil 76
column separated pentanal and the two pentanones but
not the pentanols, whereas the CP-Wax columns sepa-
rated the pentanols but not the C5 carbonyl compounds.
The distributions of carbonyl compounds and alcohols
were measured separately as well as simultaneously,
and the data were combined to derive the complete
product distribution. The rise of product concentrations
with time was almost linear over a period of 45 min.
Figure 2 shows the rise of C5 carbonyl compounds and
pentanols as a function of time to indicate the scatter of
individual data points obtained in four separate runs, in
which concentrations were measured simultaneously.
To make the data compatible, the individual rates were
normalized to a common reaction rate corresponding to
an H2O2 starting mixing ratio of 120 ppm. Additional
runs at constant reaction times were made to improve
the precision of the measurements. Table III shows the
averaged product distribution pieced together from the
results of altogether 25 runs. This distribution provides
relative product concentrations in percent of the total
observed concentration. The calculations discussed be-
low indicate the formation of other products, such as
hydroperoxides, which were not observed and are not
included.
and applied for their self-reactions values of 2 × 10−13
,
2 × 10−15, and 2.5 × 10−17 cm3 molecule−1
s
−1, re-
spectively, corresponding to known rate coefficients
for other alkylperoxyl radical self-reactions [1,17] Rate
constants for cross-combination reactions of different
types of peroxyl radicals were initially derived by tak-
ing the root over the product of the values for the self-
reactions [18]. Changes were made only if they led
to a better agreement with the observed product dis-
tributions. The branching ratios for cross-combination
reactions also are uncertain. For primary and secondary
alkylperoxyl radicals, we have initially used branching
ratios αki = 0.5 for the radical preserving channel and
0.5(1 − αki) for each channel leading to alcohols and
carbonyl compounds. Adjustments were made only if
necessary to achieve to a better simulation of the ob-
served product distribution. The reaction site of ter-
tiary peroxyl radicals lacks the hydrogen atom that
must be transferred to form a primary or secondary
alcohol so that in the interaction with primary or sec-
ondary peroxy radicals only two reaction channels ex-
ist. In these cases, the branching ratios αki = 0.4 and
(1 − αki) = 0.6 were applied in accordance with pre-
vious results [15] The rate coefficients and branch-
ing ratios for the self-reactions of ethyl peroxy and
propyl peroxyl radicals are known [1,17], and the ap-
propriate values were employed. Reactions of alkoxyl
radicals with oxygen were assigned rate coefficients
With the assumption that the mutual reactions of
n-pentylperoxyl radicals feature similar branching
ratios, one may use the observed distribution of the
pentanols to estimate relative probabilities for hydro-
gen abstraction by OH radicals at the three different
sites of n-pentane. The measured distribution for
pentan-1-ol, pentan-2-ol, and pentan-3-ol: 9.1 0.7%,
suggested by Atkinson [1]: pkO = 9.5 × 10−15 for pri-
2
mary alkoxyl, and skO = 8.0 × 10−15 cm3 molecule−1
2
s
−1 for secondary alkoxyl radicals. Reactions between
alkoxyl and alkylperoxyl radicals can be neglected. The
concentrations of peroxyl radicals are not high enough
for such reactions to compete with the other reactions
of alkoxyl radicals (with oxygen, decomposition, iso-
merization), even if very large rate coefficients were
applicable. Reactions of HO2 with alkyl peroxyl rad-
icals lead to the formation of hydroperoxides. They
56.1
1.8%, and 34.8 1.3%, indicates relative
probabilities of approximately q1 = 0.09, q2 = 0.56,
and q3 = 0.35, for the formation of pentan-1-peroxyl,
pentan-2-peroxyl, and pentan-3-peroxyl, respec-
tively, and these values were initially used in the
calculations. Other parameters were taken from our
were assigned rate coefficients kHO = 1.5 × 10−11 cm3
2
molecule−1 s−1 for C5 peroxyl radicals. The rate
coefficient for HO2 with ethyl peroxyl is known
[1,17]. Further details will be given in the Results
section.
previous study: α11 = 0.42, α22 = 0.46, α33 = 0.40,
1kisom = 4.0 × 105
s
,
2kisom = 1.1 × 105 s−1
,
−1
2kdec = 8.4 × 103 s−1
,
3kdec = 2.6 × 104 s−1 (see
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682
HEIMANN AND WARNECK
6
7
as shown in Table I (with kisom ≈ kisom ≥ 2 × 106
s
−1); decomposition reactions should be much slower
and were ignored. The ultimate products are stable
hydroxy-carbonyl compounds: 4-hydroxy-pentanal
and 1-hydroxy-pentan-4-one, respectively.
The product distribution calculated for 30 min re-
action time is presented in column (a) of Table III.
It is in surprisingly good agreement with the experi-
mental data shown in the preceding column. Obvious
differences are the higher yields of the pentanols, the
nearly equal yield of pentanal and pentan-1-ol, which
is in contrast to the observed ratio [pentanal]/[pentan-
1-ol] = 1.97 0.91, and the higher relative yield of
the sum of pentanal and pentan-1-ol compared to
the observed yield. This suggests a need for rais-
ing some of the branching ratios and lowering the
probability of pentan-1-peroxyl formation. The cal-
culations revealed that the dominant reactions in the
system are the self-reactions of pentan-2-peroxyl and
pentan-3-peroxyl radicals, their mutual interaction,
and reactions with the primary 4-hydroxy-pentan-1-
peroxyl radical that derives from the isomerization
of pentan-2-oxyl. Pentan-1-peroxyl radicals, in con-
trast, react with most of the other peroxy radicals at
nearly equal rates, but these are less important be-
cause of the lower probability at which pentan-1-
peroxyl radicals are generated. Column (b) in Table III
presents the product distribution obtained after the fol-
lowingchangesintheparameters:q1 = 0.07, q2 = 0.58,
and q3 = 0.35; α11 = α22 = 0.56, α33 = 0.50. These
changes improve the distribution between pentanols
and pentanones, but not that between pentan-1-ol and
pentanal. A better representation of the latter can be
achieved by adjusting the ratio of pentan-1-ol to pen-
tanal formed in the cross-combination reactions of
pentan-1-peroxyl radicals with secondary peroxyl radi-
calsinthesystem:pentan-2-peroxyl, pentan-3-peroxyl,
and 1-hydroxy pentan-4-peroxyl (numbers 2, 3, and
6 in Fig. 1). This required changes in the parameters
y1i and z1i that determine the distribution of carbonyl
compounds and alcohols resulting as products from
pentan-1-peroxyl radical cross reactions (see Table I).
Subsequent calculations used y12 = y13 = y16 = 0.65,
z12 = z13 = z16 = 0.35, whereas yki = zki = 0.5 was re-
tained for all other cross-combination reactions. Fi-
nally, the parameters for the initial distribution
of pentylperoxyl radicals were slightly readjusted:
q1 = 0.074, q2 = 0.58, and q3 = 0.346; the branching
ratios for the cross-combination reactions were raised
from 0.5 to 0.56, whereas the branching ratios for
the self-reactions of pentyl peroxy radicals were set
at α11 = α22 = 0.56, and α33 = 0.50. The final product
distribution, which is shown in column (c) of Table III,
Figure 2 Rise with time of the sum of pentanols and the sum
of pentanones and pentanal during the oxidation of n-pentane
(for the individual contributions of compounds, see Table III).
Data from three runs (circles, triangles, and diamonds) are
normalized to a common total reaction rate corresponding to
an initial H2O2 mixing ratio of 120 ppm. The solid lines are
calculated with parameters providing an optimal approxima-
tion of the observed product distribution (penultimate column
of Table III).
Table II). The low yield of diols found in that study
[9] had suggested that branching ratios associated
with reactions of hydroxy-pentylperoxyl radicals are
greater than those for alkylperoxyl radicals in general,
approximately α6 j ≈ α7 j ≈ 0.8 (where j = 1−7),
and this value was used. All other branching ratios
were initially set to 0.5, and it was assumed that
yki = zki = 0.5 for the cross-combination reactions
(for definitions, see Table I). The decomposition of
pentan-1-oxyl was neglected. The rate coefficient the-
oretically estimated for the split-off of formaldehyde
is small compared to that for isomerization [12], and
the butyl radical formed simultaneously should be
partly oxidized to butanal, which was not identified as
a product. The two hydroxy-pentoxyl radicals derived
from the corresponding peroxyl precursors (numbers
6 and 7 in Fig. 1) were assumed to isomerize rapidly
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PRODUCT DISTRIBUTIONS FROM THE OH RADICAL-INDUCED OXIDATION
683
Table III Oxidation of n-Pentane: Observed and Calculated Product Distributions after 30 min Reaction Time
Observed
(%)
Calculateda
Observed
a (%)
b (%)
c (%)
db
eb
Pentan-1-ol
Pentan-2-ol
Pentan-3-ol
Pentanal
Pentan-2-one
Pentan-3-one
Ethanal
Propanal
Ethanol
Propan-1-ol
Isomer. Prod.
1,4 Pentandiol
Hydroperoxidese
1.59 0.13
9.79 0.31
6.07 0.23
3.01 1.20
19.18 3.61
18.48 3.45
8.69 1.89
7.47 1.95
1.47 0.18
1.09 0.39
23.16 4.29c
–
2.70
12.17
7.57
3.40
20.19
18.18
6.70
7.90
1.41
0.35
19.42d
–
2.00
10.77
6.56
2.59
20.19
18.32
7.51
8.81
1.54
0.40
21.39d
–
1.58
10.36
6.19
3.00
19.08
18.14
7.81
8.97
1.45
0.36
23.06d
–
0.56
3.68
2.20
1.07
6.76
6.44
2.78
3.24
0.51
0.13
8.21d
0.91
17.34
0.56 0.05
3.47 0.11
2.16 0.08
1.07 0.43
6.83 1.28
6.58 1.23
3.09 0.67
2.66 0.69
0.52 0.06
0.38 0.14
8.24 1.53c
n. d.
–
–
–
–
n. d.
a See text for conditions assumed in the calculations. Columns a, b, and c give percentage distributions; results in column d (in ꢀmol mol−1
)
correspond to those in column c.
b Product distribution in units of μmol mol−1; the experimental data are adjusted to fit the same initial H2O2 concentration as in the calculations
(120 μmol mol−1); n. d. = not determined.
c Contribution of the unidentified peak seen on the CP-Sil column that is attributed to an isomerization product.
d Calculated as sum of 4-hydroxy-pentanal and 1-hydroxy-pentan-4-one.
e Pentyl-2-hydroperoxide contributes 56% and pentyl-3-hydroperoxide 35% to the total.
demonstrates that observed and calculated product dis-
tributions can be brought into reasonable agreement
simply by adjusting probabilities of pentylperoxyl rad-
ical formation and branching ratios of pentylperoxyl
reactions. It was not necessary to change rate coeffi-
cients of cross-combination reactions.
The last two columns of Table III compare
calculated and experimental product concentrations.
Hydroperoxides contribute 32% to the sum of all prod-
ucts, with 90% being due to the two secondary pentyl-
hydroperoxides; 1,4 pentan-diol contributes only 1.7%.
Neither of these has been detected by the analytical pro-
cedures employed.
It should be reiterated that the amounts of isomer-
ization products listed in Table III as having been ob-
served refer to a gas chromatographic peak occurring at
a retention time typical of C5 hydroxy-carbonyl com-
pounds that were not specified, whereas the calcula-
tions refer to the sum of 4-hydroxy-pentanal and 1-
hydroxy-pentan-4-one. Thus, the agreement between
observation and calculation refers only to the extent of
isomerization, not to the individual products that are
involved.
methyl-butan-3-ol, and ethanol. Also observed were 2-
methyl-butanal and 3-methyl-butanal, but these could
not be quantified because their peaks overlapped with
the much larger peak of 2-methyl-butan-3-one. Ac-
cordingly, their abundances could only be estimated.
Propan-2-ol, which is an expected product, could not
be observed because the corresponding peak was hid-
den underneath the much larger peak of isopentane on
both gas chromatographic columns used. Identifica-
tion of 2-methyl-butan-2-hydroperoxide as a product
was confirmed in separate experiments by adding CO
to the reaction mixture, so that some of the hydroxyl
radicals were converted to HO2, which subsequently
by reacting with 2-methyl-butan-2-peroxyl increased
the production of the tertiary hydroperoxide. This pro-
cedure has been found useful in our previous study
of the oxidation of 2,3-methyl-butane [15]. Figure 3
shows the rise of the four major products as a func-
tion of time to indicate the scatter of individual data
points. Again, the rates of individual runs were nor-
malized to a common reaction rate corresponding
to an H2O2 starting mixture of 120 ppm. Table IV
shows the percentage distribution of the observed prod-
ucts derived from seven different runs. This distribu-
tion does not include 2-methyl-butanal and 3-methyl-
butanal owing to the experimental uncertainties in their
quantification, but they are included in the last col-
umn of Table IV, which compares normalized aver-
age experimental mixing ratios with those derived by
calculations.
Isopentane
Major products appearing in the gas chromatograms
were acetone, acetaldehyde, 2-methyl-butan-2-ol,
and 2-methyl-butan-2-hydroperoxide. Additional, less
abundant products were 2-methyl-3-butanone, 2-
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684
HEIMANN AND WARNECK
Table IV Oxidation of Isopentane: Observed and Calculated Product Distributions after 30 min Reaction Time
Observed
(%)
Calculateda
Observed
eb
a
b
c
db
Acetone
Acetaldehyde
26.93 2.21
26.06 2.45
15.37 4.01
14.65 3.63
10.15 4.01
3.61 2.42
3.21 0.54
27.92
24.27
21.02
9.76
10.31
3.31
3.40
–
–
–
–
–
28.94
26.69
15.38
15.82
8.04
3.02
2.10
–
–
–
–
–
27.76
26.38
15.48
14.62
10.09
3.65
2.00
–
–
–
–
–
–
–
–
13.92
13.07
7.77
7.33
5.06
1.85
0.98
0.55
1.89
0.87
0.43
0.21
1.93
0.10
3.52
13.50 1.11
13.07 1.22
7.71 2.01
7.35 1.82
5.09 2.01
1.81 1.21
1.62 0.27
n. d
tert-Hydroperoxide
2-Methyl butan-2-ol
2-Methyl butan-3-one
2-Methyl butan-3-ol
Ethanol
Propan-2-ol
–
–
–
–
–
–
–
–
2-Methyl-butanal
3-Methyl-butanal
2-Methyl butan-1-ol
3-Methyl butan-1-ol
Isomer. Productsc
2-Methyl butan-1,4 diol
Hydroperoxidesd
1.55 0.63
1.25 0.63
n. d
n. d
n. d
n. d
n. d
–
–
–
–
–
–
a See text for conditions assumed in the calculations. Columns “a,” “b,” and “c” give percentage distributions; results in column “d” (in ꢀmol
mol−1) correspond to those in column “c.”
b Product distribution in units of ꢀmol mol−1; the experimental data are adjusted to fit the same initial H2O2 concentration as in the calculations
(120 ꢀmol mol−1); n. d. = not determined.
c Sum of 4-hydroxy 2-methyl-butanal and 4-hydroxy 3-methyl-butanal.
d Other than 2-methyl butan-2-hydroperoxide; 2-methyl butan-3-hydroperoxide is the second major contributor.
Figure 4 presents an abbreviated scheme for the
oxidation of isopentane, which forms the basis for
computer simulations. Only the major oxidation path-
ways following production of the primary peroxyl
radicals b and c are shown. The other two primary
radicals a and d, which are formed by hydrogen ab-
straction from the methyl groups of isopentane and
addition of oxygen, are assumed to react in anal-
ogy to pentan-1-peroxyl, whose reactions are shown
in Table I. The total oxidation scheme involves al-
together eight peroxyl radicals. In addition to the
six radicals a–f shown in Fig. 4, one must consider
1-hydroxy-2-methyl-butan-4-peroxyl and 1-hydroxy-
3-methyl-butan-4-peroxyl arising from isomerization
Figure 3 Rise with time of the major products: acetone, acetaldehyde, 2-methyl butan-2-ol, and 2-methyl butan-2-
hydroperoxide during the oxidation of isopentane. Data from different runs are normalized to a common total reaction rate
corresponding to an initial H2O2 mixing ratio of 120 ppm. Data obtained from the same runs are identified by circles, trian-
gles, diamonds, and asterisks, respectively. The solid lines result from calculations based on an optimal choice of parameters
(penultimate column of Table IV).
International Journal of Chemical Kinetics DOI 10.1002/kin

PRODUCT DISTRIBUTIONS FROM THE OH RADICAL-INDUCED OXIDATION
685
Figure 4 Oxidation mechanism of isopentane. Only reaction pathways evolving from tertiary 2-methyl butan-2-peroxyl and
secondary 2-methyl butan-3-peroxyl are shown. Reaction pathways for the other two peroxyl radicals initially formed (a and d)
are treated like butan-1-peroxyl (see text for details).
conceivable competing reactions. According to Batt
et al. [23], decomposition to form butan-2-one and a
methyl radical is negligible in comparison to acetone
and ethyl as products. Indeed, we have not observed
butane-2-one among the products. The rate coefficient
for the decomposition of 2-methyl-butan-3-oxyl has
not yet been determined, but we can safely assume
that its value is similar to, or even larger than, that
for butan-2-oxyl, which has been repeatedly studied.
In this case, the experimental data [10,20,21,24] aver-
age to 2.2 × 104 s−1, which agrees well with the value
derived theoretically [13], 3.5 × 104 s−1. The initial
decomposition constant adopted in the computer sim-
ulations was ckdec = 4.5 × 104 s−1, but subsequently it
was found necessary to raise the value so as to achieve
a better representation of acetaldehyde production.
The observed product distribution does not allow
to estimate the relative probabilities for hydrogen
atom abstraction from isopentane in the same manner
as for n-pentane, not only because the products
resulting from abstraction at the methyl groups
were not quantified, but also because acetone and
acetaldehyde derive from both of the two pre-
cursor radicals b and c. The formulas of Greiner
[4] and Atkinson [5,6] suggest 12.7% or 11.2%,
of the corresponding 2-methyl-butan-1-oxyl and 3-
methyl-butan-1-oxyl precursors. The first of these was
assumed to isomerize at the same rate as butan-1-oxyl,
which has been well studied, experimentally [19–22]
as well as theoretically [14]. In this case, the iso-
merization rate coefficient has an average value of
1.6 × 105 s−1. Isomerization of 3-methyl-butan-1-oxyl
should be twice as rapid because two methyl groups
are available for internal hydrogen abstraction. Ac-
a
cordingly, rate coefficients of kisom = 1.6 × 105 s−1
d
and kisom = 3.2 × 105 s−1, respectively, were applied
for the isomerization of these radicals. The calcula-
tions show, however, that reactions and products within
the two branches starting from the radicals a and d in
Fig. 4 make only a minor contribution to the overall
mechanism.
The reaction sequences shown in Fig. 4 involve
the decomposition of 2-methyl-butan-2-oxyl and 2-
methyl-butan-3-oxyl. For the first process, which leads
to acetone and an ethyl radical, Me´reau et al. [13] have
calculated a decomposition constant bkdec = 9.4 × 105
s
−1. Batt et al. [23] had earlier reported experimen-
tal data obtained at elevated temperatures that when
extrapolated to 298 K lead to 1.6 × 104 s−1. Both val-
ues are large enough to preclude the interference by
International Journal of Chemical Kinetics DOI 10.1002/kin

686
HEIMANN AND WARNECK
respectively, for hydrogen abstraction at the three
methyl groups combined. We have adopted an inter-
mediate value of 12% in the computer simulations,
so that qa = 0.08 and qd = 0.04. Initial values for
the probabilities of formation of tertiary and sec-
ondary peroxyl radicals were derived as follows: The
ratio qb/qc is approximately given by the sum of
acetone, 2-methyl-butan-2-ol, and 2-methyl-butan-2-
hydroperoxide minus the fraction of acetone resulting
from decomposition of the 2-methyl-butan-3-oxyl
radical, divided by the sum of 2-methyl-butan-3-one
and 2-methyl- butan-3-ol, corrected for the fraction
of decomposition of 2-methyl-butan-3-oxyl. From the
observed product distribution in Table IV, we estimate
that qb/qc ≈ (56.95 − 3.61)/(13.76 + 3.61) = 3.07;
the additional condition qb + qc = 0.88 then leads
to qb ≈ 0.66 and qc ≈ 0.22. These parameters were
initially used in the computer simulations.
tions of secondary peroxy radicals were raised slightly
to αss = αsp = 0.55. The last two columns in Table IV
compare calculated and scaled experimental product
mixing ratios after 30 min reaction time. Ethanol is the
only product, which is significantly underrepresented
in the final calculation. This is caused by the impor-
tant role of CH3CH2OO• radicals in the formation of
2-methyl-butan-2-ol by reacting with 2-methyl-butan-
2-peroxyl. The situation would improve, if 2-methyl-
butan-3-peroxyl radicals would share in this role. This
may be accomplished by setting kpt = 4.0 × 10−15 and
kst = 4.0 × 10−16 cm3 molecule−1
s
−1, but in this case
the decomposition constant of 2-methyl-butan-3-oxyl
would have to be raised to ckdec ≈ 1.5 × 105 s−1 in or-
der to obtain a product distribution in harmony with the
experimental data.
Column (a) of Table IV presents the product distri-
bution calculated with the parameters discussed above.
Comparison with the experimental data shows that the
rate of production of 2-methyl-butan-2-hydroperoxide
is calculated too high and that of 2-methyl-butan-2-
ol is too low. The production of acetaldehyde also is
somewhat low. Trial calculations made evident that the
rate of the tertiary hydroperoxide production can be
lowered only by decreasing the rate coefficient for the
reaction between HO2 and 2-methyl-butan-2-peroxyl
DISCUSSION
Three aspects deserve discussion: one is the relative
probability of hydrogen abstraction, another deals with
the branching ratios associated with the mutual reac-
tions of pentylperoxy radicals, and the third concerns
the comparison of observed and calculated product
distributions.
n-Pentane
(radical b in Fig. 4) from kHO = 1.5 × 10−11, used ini-
2
tially, to kHO = 6.0 × 10−12, and this value was sub-
Relative probabilities for hydrogen abstraction at dif-
ferent sites of n-pentane were derived from the dis-
tribution of the alcohols and from a comparison of
calculated product distributions with the experimental
data. The former results are, in percent, q1 = 9.1 0.7,
q2 = 56.1 1.8, and q3 = 34.8 1.3, whereas the lat-
ter are 7.4, 58.0, and 34.6, respectively. Both corre-
spond rather closely to the probabilities calculated with
the algorithm for alkanes proposed by Atkinson [5,6],
which gives 9.4%, 55.1%, and 35.5%. This contrasts
with results obtained with the formulas developed by
Greiner [4], which lead to 10.4%, 59.7%, and 29.9%. It
is remarkable that the present observations and the the-
oretical predictions, which are based on a few selected
hydrocarbons that did not include n-pentane, provide
such a good agreement. In addition, the individual rate
coefficients calculated by using the method of Atkinson
2
sequently applied. The rate of formation of 2-methyl-
butan-2-ol is primarily determined by the interaction of
2-methyl-butan-2-peroxyl with ethyl-peroxyl, and to a
lesser extent with 2-methyl-butan-3-peroxyl (radicals e
and c in Fig. 4). Accordingly, the rate coefficient for the
reaction between primary and tertiary peroxy radicals
was increased from 2.0 × 10−15 cm3 molecule−1 s−1
used initially to kpt = 6.0 × 10−15 cm3 molecule−1 s−1
.
The rate coefficient for the decomposition of the 2-
methyl-butan-3-oxyl radical was also increased from
the initial value 4.5 × 104 s−1 to ckdec = 8.5 × 104 s−1
.
These changes in the parameters resulted in the prod-
uct distribution shown in column (b) of Table IV. The
production rates of 2-methyl-butan-2-ol and 2-methyl-
butan-2-hydroperoxide compare more favorably with
the experimental data, and that of acetaldehyde has
also improved. However, the rates of formation of 2-
methyl-butan-3-one and 2-methyl-butan-3-ol are too
low, indicating a need for readjustment of the proba-
bilities for hydrogen abstraction from isopentane. The
values qb = 0.60 and qc = 0.28 were found to provide a
product distribution that compares well with the exper-
imental data. In the final fit, which is shown in Table IV
incolumn(c), thebranchingratiosassociatedwithreac-
sum to a total kOH = 3.9 × 10−12 cm3 mol−e1c2ule−1 s−1
,
close to the measured value [1,2] 4.0 × 10 , whereas
the formulas of Greiner lead to 3.7 × 10−12 cm3
molecule−1 −1. The Kwok and Atkinson [6] estima-
s
tion method is based on a much larger data base for re-
actions of OH with alkanes than the earlier calculation
by Greiner [4]. Hence, it is able to take into account the
effect of near neighbors and should be more accurate.
International Journal of Chemical Kinetics DOI 10.1002/kin

PRODUCT DISTRIBUTIONS FROM THE OH RADICAL-INDUCED OXIDATION
687
The branching ratios for the self-reactions of n-
pentan-2-peroxyl and n-pentan-3-peroxyl radicals that
were needed to bring the calculated fractions of pen-
tanols and pentanones into agreement with the ex-
perimental data are higher than those that we had
derived previously [9], although still within the mu-
tual range of uncertainty. Independent of the model
calculations, the product ratios R1 = pentanal/pentan-
1-ol, R2 = pentan-2-one/pentan-2-ol, and R3 = pentan-
3-one/pentan-3-ol can be used to estimate effective
branching ratios for each of the n-pentan-peroxyl
isomers involved. The subscripts refer again to
the numbers assigned to the radicals shown in
Fig. 1. Effective branching ratios can be calculated
from α¯i = (Ri − 1)/(Ri − 1 + 2 fi ), where i = 1, 2, or
previously noted [9] that the reactions following the
generation of pentan-2-peroxyl radicals produce more
acetaldehyde than can be accounted for by the decom-
position of propan-2-oxyl, and we had suggested that
decomposition of the product arising from isomeriza-
tion of 4-hydroxy pentan-1-oxyl (7kisom; see Table I)
might be responsible for it.
While the calculations seem to predict correctly the
total amount of isomerization products, it must again
be cautioned that we have not identified these products
experimentally. As the major isomerization product de-
rives from pentan-2-oxyl, the agreement between cal-
culated and experimental data confirms the magnitude
2
of the isomerization constant used, kisom = 1.1 × 105
s
−1. In our previous study [9] of the decomposition of
i
i
3, and fi = (1 + kdec/kO [O2] + kisom/kO [O2])−1
iodopentanes, the product assigned to isomerization of
the pentan-2-oxyl radical appeared to be unstable giv-
ing rise to a number of other products. In the present
experiments, onlyonemajorisomerizationproductwas
detected. Thelowyieldofpentan-1-olissurprising, and
our attempt to rationalize it by lowering the fraction of
pentan-1-peroxyl radicals entering into the pentan-1-ol
forming channel requires further scrutiny.
2
2
refers to decomposition, isomerization and reaction
with oxygen of the corresponding n-pentoxyl radical.
TheexperimentaldatainTableIIIprovide R1 = 1.97
0.92, R2 = 1.96 0.43, and R3 = 3.07 0.68. Rela-
tive rate coefficients i kdec/kO [O2] and i kisom/kO [O2]
2
2
are taken from our previous determination [9] (see
Table II), including the respective error margins.
With the above data, one obtains α¯1 = 0.54 0.35,
α¯2 = 0.60 0.14, and α¯3 = 0.59 0.10. These aver-
age branching ratios are larger than those that were
needed to calculate a product distribution compati-
ble with the experimental data. The difference prob-
ably reflects the influence of the fairly large branch-
ing ratio adopted in the calculations for reactions of
4-hydroxy-pentan-1-peroxyl and 1-hydroxy-pentan-4-
peroxyl radicals.
Table III shows that by using branching ratios in the
range 0.50–0.57 the calculated product distribution can
be made to agree well with that derived experimentally.
Propan-1-ol is the only exception. In this case the ob-
served amount is higher than calculated. As the only
source of propanol are reactions of propan-1-peroxyl,
generated by the decomposition of n-pentan-2-oxyl,
the amount of propanol formed depends only on the
parametersq2 and2kdec. Bothleavelittleroomforvaria-
tion. In the case of ethanol, the calculated and observed
values coincide. We consider it unlikely that propan-
1-peroxyl and ethyl peroxyl would behave much dif-
ferently. Therefore, the amount of propan-1-ol derived
from the experiments must have been overestimated.
The data in Table III also indicate a slight mismatch
between experiments and calculations for acetaldehyde
and propanal, although the experimental scatter is con-
siderable in both cases, and the calculated values are
within the experimental error ranges. Decomposition
of pentan-2-oxyl and pentan-3-oxyl yields acetalde-
hyde and propanal in nearly equal amounts, yet the ex-
periments indicate an excess of acetaldehyde. We had
Isopentane
It was not possible to derive from the observed product
distribution the relative probabilities for hydrogen ab-
straction at all four sites of isopentane. The probability
for H-atom abstraction at the methyl groups was esti-
mated with the formulas presented by Atkinson [5,6]
and Greiner [4] as ∼12%. The relative probabilities
for the formation of 2-methyl- butan-2-peroxyl and 2-
methyl-butan-3-peroxyl were then obtained by com-
parison of simulated and observed product distribu-
tions. This procedure leads to qa = 8.0%, qb = 60.0%,
qc = 28.0%, and qd = 4.0%. This compares well with
probabilities calculated from the algorithm proposed
by Atkinson [5,6], which are 7.43%, 60.85%, 28.0%,
and 3.72%, respectively, whereas the formulas of
Greiner [4] give 8.4%, 63.0%, 24.4%, and 4.2%. As
in the case of n-pentane, we can calculate the total
rate constant by summing the individual rate constants.
The algorithm of Atkinson [5,6] gives for isopen-
tane kOH = 3.87 × 10−12 cm3 molecule−1 s−1, which is
close to the measured value 3.7 × 10−12 [1], whereas
the formulas of Greiner [4] lead to 4.57 × 10−12 cm3
molecule−1 −1. The present results obviously are in
s
better agreement with Atkinson’s method of estimat-
ing probabilities for hydrogen abstraction than with
Greiner’s, for both n-pentane and isopentane. How-
ever, the former method is based on a larger data base
and takes into account the effects of nearest neighbors
so that it should be more accurate.
International Journal of Chemical Kinetics DOI 10.1002/kin

688
HEIMANN AND WARNECK
The product distribution obtained from the oxida-
tion of isopentane is dominated by acetone and ac-
etaldehyde. The source of both is primarily the decom-
position of 2-methyl- butan-2-oxyl and the subsequent
interaction of ethyl peroxyl with 2-methyl-butane-2-
peroxyl, which consumes approximately 56% of the
former and 42% of the latter peroxy radical. Approx-
imately 73% of both products, acetone and acetalde-
hyde, are formed along this pathway. The remainder
derives from the decomposition of 2-methyl-butan-3-
oxyl. The large fraction of 2-methyl-butan-2-ol among
the products demonstrates the importance of reactions
between 2-methyl-butan-2-peroxyl and the other per-
oxyl radicals, of which CH3CH2OO• and 2-methyl-
butan-3-peroxyl are dominant. This is in contrast to
the case of 2,3 dimethyl butane oxidation studied by us
previously [9], where the rate of tertiary alcohol forma-
tion was much lower. In order to bring calculated and
observed rates of 2-methyl-butan-2-ol formation into
agreement, it is necessary to increase the rate coeffi-
cients of these reactions by at least a factor of two, but
this has the consequence that the calculated amount of
ethanol is smaller than the observed one. On the other
hand, with regard to the reaction between HO2 and 2-
methyl butan-2-peroxyl, the rate coefficient required
to bring the calculated fraction of 2-methyl- butan-2-
hydroperoxide into agreement with the observed one is
similar to that applied previously for 2, 3-dimethyl bu-
tane. Of special interest is the magnitude of the decom-
position constant for the 2-methyl butan-3-oxyl radical.
The present results suggest a value of ckdec ≈ 8.5 × 104
The experimental part of this study was a contribution to the
EUROTRAC project LACTOZ. We thank H.-J. Benkelberg
for carrying out a few supplementary experiments.
BIBLIOGRAPHY
1. Atkinson, R. J Phys Chem Ref Data 1997, 26, 215–290.
2. Atkinson, R.; Arey, J. Chem Rev 2003, 103, 4605–4638.
3. Orlando, J. J.; Tyndall, G. S.; Wallington, T. J. Chem
Rev 2003, 103, 4657–4689.
4. Greiner, N. R. J Chem Phys 1970, 53, 1070–1976.
5. Atkinson, R. Int J Chem Kinet 1987, 19, 799–828.
6. Kwok E. C. S.; Atkinson, R. Atmos Environ 1995, 29,
1685–1696.
7. Do´be´, S.; Be´rces, T.; Ma´rta, F. Int J Chem Kinet 1986,
18, 329–344.
8. Atkinson, R.; Kwok, E. S. C.; Arey, J.; Aschman, S.
Faraday Discuss 1995, 100, 23–37.
9. Heimann, G.; Benkelberg, H. J.; Bo¨ge, O.; Warneck, P.
Int J Chem Kinet 2002, 34, 126–138.
10. Meunier, N.; Doussin, J. F.; Chevallier, E.; Durand-
Jolibois, R.; Picquet-Varrault, B.; Carlier, P. Phys Chem
Chem Phys 2003, 5, 4834–4839.
11. Atkinson, R. Int J Chem Kinet 1997, 29, 99–111.
12. Somnitz H.; Zellner, R. Phys Chem Chem Phys 2000, 2,
1907–1918; 4319–4325.
13. Me´reau, R.; Rayez, M. T.; Caralp F.; Rayez, J. C. Phys
Chem Chem Phys 2000, 2, 3765–3772.
14. Me´reau, R.; Rayez, M. T.; Caralp, F.; Rayez, J. C. Phys
Chem Chem Phys 2003, 5, 4828–4833.
15. Heimann, G.; Warneck, P. J Phys Chem 1992, 96, 8403–
8409.
16. Curtis, A. R.; Sweetenham, W. P. Facsimile/Checkmat
Users Manual; Aere-R-12805, Her Majesty’s Stationary
Office: London; 1988.
17. Lightfoot, P. D.; Cox, R. A.; Crowley, J. N.; Destriau, M.;
Hayman, G. D.; Jenkin, M. E.; Moortgat, G. K.; Zabel,
F. Atmos Environ 1992, 26A, 1805–1964.
18. Madronich, S.; Calvert, J. G. J Geophys Res 1990, 95,
5697–5715.
19. Carter, W. P. L.; Lloyd, A. C.; Sprung, J. L.; Pitts, J. N.,
Jr. Int J Chem Kinet 1979, 11, 45–101.
20. Cox, R. A.; Patrick, K. F.; Chant, S. A. Environ Sci
Technol 1981, 15, 587–592.
21. Niki, H.; Maker, P. D.; Savage, C. M.; Breitenbach, L.
P. J Phys Chem 1981, 85, 2698–2700.
s
−1, although it might be greater. The present results
also confirm the conclusions derived by Batt et al. [23],
who had found that the 2-methyl-butan-2-oxyl radi-
cal decomposes overwhelmingly to form acetone and
ethyl, whereas the alternative decomposition pathway
resulting in butan-2-one and a methyl radical is unim-
portant in comparison. The fate of the primary per-
oxyl radicals formed by hydrogen abstraction from the
methyl groups of isopentane and the alkoxyl radicals
appearing in the corresponding oxidation chains could
not be explored and remains undetermined.
22. Heiss, A.; Sahetchian, K. Int J Chem Kinet 1996, 28,
531–544.
SUPPLEMENTARY INFORMATION
23. Batt, L.; Islam, T. S. A.; Rattray, G. N. Int J Chem Kinet
1978, 10, 931–943.
24. Libuda, H. G.; Shestakov, O.; Theloke, J.; Zabel, F. Phys
Chem Chem Phys 2002, 4, 2579–2586.
Computer programs containing the complete reaction
mechanisms for the oxidation of n-pentane and isopen-
tane are available from the corresponding author.
International Journal of Chemical Kinetics DOI 10.1002/kin