Determination of the hydroxy nitrate yields from the reaction of C2-C6 alkenes with OH in the presence of NO

Article abstract of DOI:10.1021/jp982320z

The yields of hydroxy nitrates from the reaction of selected C₂-C₆ alkenes with OH in the presence of NO were measured at 296 ± 3 K in a 9600 L photochemical smog chamber. Hydroxyl radicals were produced from the photolysis of isopropyl nitrite in the presence of NO. The loss of the alkene was followed using gas chromatography. The hydroxy nitrate products were determined using a combination of capillary chromatography and an organic nitrate specific chemiluminescence detector. The yield of hydroxy nitrates was observed to increase with the size of the precursor alkene as follows: ethene (0.86%), propene (1.5%), 1-butene (25%), cis-2-butene (3.4%), and 1-hexene (5.5%). Previous studies involving the production of alkyl nitrates from alkanes show a similar trend, but the yields reported here are a factor of 2-3 lower than for the corresponding simple alkylperoxy radical. The impact of a β-hydroxy group on the nitrate yield is examined using an ab initio molecular orbital study. It indicates that a hydrogen-bonded peroxy nitrite intermediate is formed, which results in a decrease in D₀(O-O) for the peroxy linkage of about 8 kJ/mol. This would be expected to effectively decrease the organic nitrate yield. The implications of these findings for the organic nitrate path as an atmospheric NO_x removal mechanism are discussed.

Full text of DOI:10.1021/jp982320z

J. Phys. Chem. A 1998, 102, 8903-8908
8903
Determination of the Hydroxy Nitrate Yields from the Reaction of C2-C6 Alkenes with OH
in the Presence of NO
Jason M. O’Brien,† Eva Czuba,† Donald R. Hastie,† Joseph. S. Francisco,‡ and
Paul B. Shepson*,†,‡
Department of Chemistry and Centre for Atmospheric Chemistry, York UniVersity, 4700 Keele Street,
North York, Ontario, Canada, M3J 1P3, and Departments of Chemistry and Earth and Atmospheric Sciences,
Purdue UniVersity, 1393 Brown Building, West Lafayette, Indiana 47907-1393
ReceiVed: May 20, 1998; In Final Form: August 31, 1998
The yields of hydroxy nitrates from the reaction of selected C2-C6 alkenes with OH in the presence of NO
were measured at 296 ( 3 K in a 9600 L photochemical smog chamber. Hydroxyl radicals were produced
from the photolysis of isopropyl nitrite in the presence of NO. The loss of the alkene was followed using gas
chromatography. The hydroxy nitrate products were determined using a combination of capillary chroma-
tography and an organic nitrate specific chemiluminescence detector. The yield of hydroxy nitrates was
observed to increase with the size of the precursor alkene as follows: ethene (0.86%), propene (1.5%), 1-butene
(2.5%), cis-2-butene (3.4%), and 1-hexene (5.5%). Previous studies involving the production of alkyl nitrates
from alkanes show a similar trend, but the yields reported here are a factor of 2-3 lower than for the
corresponding simple alkylperoxy radical. The impact of a â-hydroxy group on the nitrate yield is examined
using an ab initio molecular orbital study. It indicates that a hydrogen-bonded peroxy nitrite intermediate is
formed, which results in a decrease in D0(O-O) for the peroxy linkage of about 8 kJ/mol. This would be
expected to effectively decrease the organic nitrate yield. The implications of these findings for the organic
nitrate path as an atmospheric NOx removal mechanism are discussed.
Introduction
For the most part, oxidation of alkenes by OH proceeds via
addition to one of the double bond carbons, producing a
â-hydroxyalkylperoxy radical.3 In contrast to the situation for
alkylperoxy radicals, there is very little published data regarding
organic nitrate yields for reaction of these radicals with NO.
This is in part due to the difficulty in obtaining pure standards,
as well as in making measurements of these relatively polar
and thus adsorptive species.4 The production of â-hydroxyalkyl
nitrates is potentially very important because the hydroxy group
increases the water solubility,5 and thus, the atmospheric
lifetimes of these nitrates are much shorter than those of the
analogous alkyl nitrates. Because of the wide range of reactive
atmospheric alkenes and alkanes that exist and the experimental
difficulty in measuring yields, it is desirable to have a firm
understanding of the structural features that influence the
branching ratio for reaction 1 so that a predictive capability can
be developed.
Ozone production in the troposphere involves an OH-
catalyzed oxidation of hydrocarbons in the presence of nitrogen
oxides.1 Although the overall features for this process are well
documented, many details remain uncertain, including the role
of this process in mediating the ultimate removal of nitrogen
oxides from the atmosphere. The major loss process of
hydrocarbons emitted into the atmosphere is through the reaction
•
with the OH radical to produce a peroxy radical (RO2 ). The
peroxy radical can then react with NO in two pathways:
RO2 + NO f RO• + NO2
(1a)
(1b)
•
f RONO2
Reaction 1a, which results in tropospheric ozone formation via
the subsequent photolysis of NO2, is the major pathway, while
the production of the organic nitrate (RONO2) in reaction 1b is
a relatively minor pathway. However, reaction 1b can signifi-
cantly impact the production and distribution of tropospheric
ozone, since it represents a sink for both the precursor peroxy
radicals and NOx. Thus, the branching ratio of reaction 1a to
reaction 1b has an impact on the chain length in the chemistry
that produces O3 and an impact on the distribution and long-
range transport of tropospheric NOx. The yields (k1b/(k1a + k1b))
of alkyl nitrates from RO2 radicals produced from the OH
reaction with a number of alkanes have been determined and
found to increase with the size of the R group and to increase
with increasing pressure and decreasing temperature.2
To date the only published â-hydroxyalkyl nitrate yields are
for the following alkenes: propene, 1.6%;6 cis-2-butene, 3.6%;4
isoprene, 4.4%7 and 8-13%.8
Alkyl and â-hydroxyalkyl nitrate ambient concentrations have
been determined in several field studies.9-18 The measurement
of organic nitrates can provide information about the extent of
photochemical processing of an air mass, as well as information
regarding the nature of the peroxy radicals responsible for ozone
production, if the yields are accurately known.15,16,18 Since there
are only a few determined yields for â-hydroxy nitrate forma-
tion, the impact of the oxidation of alkenes on tropospheric
ozone is less certain. In this paper we present a two-pronged
analysis of â-hydroxy nitrate production. We have produced
new measurement data for the â-hydroxy nitrate yield from the
OH-radical oxidation of several alkenes. To aid in interpretation
† York University.
‡ Purdue University.
10.1021/jp982320z CCC: $15.00 © 1998 American Chemical Society
Published on Web 10/13/1998

8904 J. Phys. Chem. A, Vol. 102, No. 45, 1998
O’Brien et al.
Figure 1. Schematic diagram of the smog chamber and sampling system.
of the structural dependence of this yield, an ab initio molecular
orbital computational study of the stability of the intermediate
peroxy nitrite species was undertaken.
containing a 30 m megabore HP-1701 column and equipped
with a six-port valve and a 0.5 cm3 sample loop for direct gas-
phase sampling and injection. Detection of organic nitrates was
accomplished using a nitrate-specific detector.19 The nitrate
detector functions by thermally decomposing the chromato-
graphically separated organic nitrates, which quantitatively
converts them to NO2, which is then detected using a luminol-
based NO2 detector.19 Calibration of the entire nitrate detection
system was performed using both standard samples containing
known concentrations of the target â-hydroxy nitrate in Teflon
bags and using a flowing mixture of isopropyl nitrate in N2
from a standard 10.2 ppm cylinder (Matheson gas), diluted to
low concentrations with laboratory-generated clean air. Iso-
propyl nitrate calibration is more convenient and, since all
organic nitrates are detected with identical instrumental sensitiv-
ity,19 acts as a satisfactory surrogate calibration standard.
Experimental Section
The oxidations of the alkenes ethene, propene, 1-butene, cis-
2-butene, and 1-hexene in synthetic air mixtures were separately
investigated in a ∼9600 L cylindrical Teflon photochemical
reaction chamber, shown schematically in Figure 1. The
contents of the chamber were irradiated by 310-400 nm
radiation from 24 black lamps and mixed using a Teflon fan.
Experiments involved irradiating mixtures of isopropyl nitrite
(used as the OH source19), the test alkene, and NO in air, with
measurement of both the alkene consumed and organic nitrate
produced.
In the case of ethene as the test alkene, the following reactions
occur:
Experiments were typically conducted with initial concentra-
tions from 75 to 200 ppm of alkene, 200-500 ppm of NO, and
75 ppm of isopropyl nitrite. The alkenes (with the exception
of 1-hexene) and the NO were added into the chamber using
calibrated Tylan mass flow controllers. Care was taken to limit
the amount of NO2 added to the chamber, since it can interfere
in the determination of the branching ratio by promoting the
production of organic nitrate via alkoxy radical reaction with
NO2. Therefore, the NO was added in a large excess of N2 to
minimize the reaction of NO with O2, which is second order in
NO. The isopropyl nitrite (and 1-hexene) was added by
injecting the liquid into a stream of clean air entering the
chamber. The contents of the chamber were allowed to mix
(with the lights off) for a period of at least 1 h before initial
concentrations/blanks were determined. The lamps were then
turned on for irradiation periods ranging from 30 s to 20 min,
depending on the initial reactant concentrations. Determination
of the alkene and â-hydroxy nitrate concentrations was under-
taken while the lights were switched off. This procedure was
repeated up to 10 times for each experiment. Because the time
required for the chromatographic separation of the nitrate
products was much longer than that for the reactant alkene,
replicate alkene determinations were performed to decrease the
measurement uncertainty so that small conversions (∼5% per
CH3CH(ONO)CH3 + hV f CH3CH(O•)CH3 + NO (2)
CH3CH(O•)CH3 + O2 f CH3C(O)CH3 + HO2 (3)
HO2 + NO f NO2 + OH
(4)
(5)
OH + CH2dCH2 + O2 f CH2(OH)CH2OO•
CH2(OH)CH2OO• + NO f CH2(OH)CH2O• + NO2 (6a)
f CH2(OH)CH2ONO2 (6b)
Here, the OH radicals are generated in reactions 2-4 and the
product â-hydroxy nitrate (nitrooxy ethanol) is produced in
reaction 6b. Alkene concentrations were monitored using an
HP 5890 series II gas chromatograph equipped with a flame
ionization detector. Injection was achieved using a six-port
valve and 0.8 cm3 sample loop, and separation was achieved
using a 30 m megabore HP Al2O3 column. The â-hydroxy
nitrates (with the exception of the ethene and one of the
1-hexene experiments) were quantified using a Varian 3300 GC

Hydroxy Nitrate Yields
J. Phys. Chem. A, Vol. 102, No. 45, 1998 8905
Figure 3. Yield of hydroxy nitrates from OH reaction with propene.
vibrational frequency calculations were performed on each
optimized geometry to verify that it was a minimum-energy
structure.
Figure 2. Yield of hydroxy nitrates from OH reaction with ethene.
photolysis period) for the reactant hydrocarbon could be used.
Because air was removed from the chamber for analysis, up to
5 L min-1 (∼3%/h) of clean air was added to maintain the
chamber at atmospheric pressure.
One possible source of systematic error is that the hydroxy
alkoxy radical produced in reaction 6a could react, under high
NO2 concentrations, to also produce the â-hydroxy nitrate, as
shown in reaction 7 for the ethene system:
Results and Discussion
The alkene and product mixing ratios were corrected for
dilution flow of clean air entering the chamber (0-5 L/min)
and the â-hydroxy nitrates for secondary removal by the OH
radical,27 using OH radical reaction rate coefficients calculated
using the method described in Kwok and Atkinson.28 In the
worst case for secondary consumption, the correction factor was
determined to be 1.05. The yield of â-hydroxy nitrates (HN)
from the precusor alkene (i.e., k1b/(k1a + k1b)) is determined as
follows. Assuming that OH attack on the alkene produces
exclusively an RO2 radical by addition (this could cause as much
as a ∼10% error for 1-hexene3) and that this radical is lost by
reaction with NO, we can write
CH2(OH)CH2O• + NO2 f CH2(OH)CH2ONO2 (7)
This problem would be more severe for peroxy radicals that
have smaller branching ratios for reaction 1b so that reaction 7
would make a larger contribution to the observed organic nitrate
concentration. To minimize the NO2 concentration and therefore
the possible effects of this interfering reaction, the experiments
involving ethene (and an experiment with 1-hexene for com-
parison) were conducted at significantly lower initial reactant
concentrations. At these lower concentrations the analytical
method used for the quantitation of the â-hydroxy nitrate
products required sample concentration. In this case the
â-hydroxy nitrate products were quantified by concentrating a
1-2 L sample of chamber air on 5 mg of activated charcoal.20
These charcoal traps were extracted with 100 µL of a 50:50
mixture of acetone and benzene, and a 5 µL aliquot of this
extract was directly injected into the GC with the specific nitrate
detector. In this case calibration was conducted using known
concentration liquid standards.
The â-hydroxy nitrates needed for calibration and for retention
time determination were synthesized in the laboratory using
previously described synthesis procedures.4 The isopropyl nitrite
was synthesized according to the procedure described by
Noyes.21 Ethene, propene, 1-butene, and cis-2-butene were
obtained from Matheson, and 1-hexene was acquired from
Aldrich. These reagents all had quoted purities of 99% and
were used without further purification.
•
-d[alkene]/dt ) k1[RO2 ][NO]
and
•
d[HN]/dt ) k1b[RO2 ][NO]
Therefore, ∆[HN]/(-∆[alkene]) ) k1b/k1. In Figure 2 we have
plotted the results of all three ethene experiments as ∆[nitrooxy
ethanol] vs ∆[ethene]. The best-fit linear regression slope,
forced through zero, gives a â-hydroxy nitrate yield of (8.6 (
0.04) × 10-3 (0.86%), where the stated uncertainty is the 95%
confidence interval for the slope. For the larger 1-alkenes, the
OH radical can add to either carbon of the double bond, leading
to the formation of two different â-hydroxy nitrates. In Figure
3 we present the sum of the two organic nitrate concentrations,
2-nitrooxy propanol and 1-nitrooxy-2-propanol, plotted against
-∆[propene] for three separate propene experiments; the slope
then gives the overall yield of â-hydroxy nitrates from the OH
reaction with propene as (1.5 ( 0.1) × 10-2. The individual
isomeric organic nitrate product yields (which are equal to Rk1b/
(k1a + k1b), where R is the fraction of the OH-propene reactions
that produce the appropriate precursor peroxy radical) for
production of 2-nitrooxy propanol and for 1-nitrooxy-2-propanol
All ab initio molecular orbital calculations were performed
using the GAUSSIAN 94 program.22 Geometry optimizations
were carried out for all structures using Schlegel’s method23 to
better than 0.001 Å for bond lengths and 0.01° for angles.
Optimizations were performed with second-order Møller-
Plesset (MP2) perturbation theory23,24 and with the Becke’s
nonlocal three-parameter exchange with the Lee-Yang-Parr
correlation functional (B3LYP) density functional method.25 The
energies were refined using the G2MP2 method.26 Harmonic
were found to be (8.5 ( 0.08) × 10-3 and (6.7 ( 0.10) × 10-3
,
respectively. The difference in yields between the isomers
reflects a combination of the preferential tendency for OH
addition to the terminal carbon atom3 and the difference in
branching ratios of the primary and secondary peroxy radicals
in reaction 1.2 For propene it has been estimated that OH adds

8906 J. Phys. Chem. A, Vol. 102, No. 45, 1998
O’Brien et al.
TABLE 1: Initial Conditions and Product Yields for Each Experiment
initial
[alkene], ppm
approx initial
[NO], ppm
approx initial
[isopropyl nitrite], ppm
hydroxy nitrate
product
% yield
((95% CI)
previous
studies
test alkene
ethene no. 1a
ethene no. 2a
ethene no. 3a
overall ethene
propene no. 1
2.3
2
2.1
2.3
2.1
2.2
25
25
25
nitrooxy ethanol
nitrooxy ethanol
nitrooxy ethanol
nitrooxy ethanol
1-nitrooxy-2-propanol
2-nitrooxy-1-propanol
combined
1-nitrooxy-2-propanol
2-nitrooxy-1-propanol
combined
1-nitrooxy-2-propanol
2-nitrooxy-1-propanol
combined
1-nitrooxy-2-propanol
2-nitrooxy-1-propanol
combined
1-nitrooxy-2-butanol
2-nitrooxy-1-butanol
combined
1-nitrooxy-2-butanol
2-nitrooxy-1-butanol
combined
1-nitrooxy-2-butanol
2-nitrooxy-1-butanol
combined
1-nitrooxy-2-butanol
2-nitrooxy-1-butanol
combined
2-nitrooxy-3-butanol
1-nitrooxy-2-hexanol
2-nitrooxy-1-hexanol
combined
1-nitrooxy-2-hexanol
2-nitrooxy-1-hexanol
combined
1-nitrooxy-2-hexanol
2-nitrooxy-1-hexanol
combined
1-nitrooxy-2-hexanol
2-nitrooxy-1-hexanol
combined
0.86 ( 0.04
0.85 ( 0.07
0.89 ( 0.11
0.86 ( 0.03
0.64 ( 0.07
1.0 ( 0.1
1.6 ( 0.1
0.57 ( 0.04
0.88 ( 0.07
1.5 ( 0.1
0.67 ( 0.10
0.85 ( 0.08
1.5 ( 0.1
0.62 ( 0.04
0.92 ( 0.05
1.5 ( 0.1
1.0 ( 0.1
1.4 ( 0.3
2.4 ( 0.4
1.1 ( 0.1
1.5 ( 0.2
2.6 ( 0.2
1.3 ( 0.3
1.5 ( 0.1
2.8 ( 0.3
1.1 ( 0.1
1.4 ( 0.1
2.5 ( 0.2
3.4 ( 0.5
2.3 ( 0.9
3.1 ( 1.1
5.4 ( 1.9
1.6 ( 0.7
4.3 ( 1.1
5.9 ( 1.0
0.82 ( 0.35
6.2 ( 1.1
7.0 ( 1.4
2.3 ( 0.5
3.2 ( 0.7
5.5 ( 1.0
80
100
120
200
400
300
75
75
75
1.66
1.66
1.66
1.66
propene no. 2
propene no. 3
overall
propene
1-butene no. 1
1-butene no. 2
1-butene no. 3
230
210
230
500
500
500
75
75
75
overall
1-butene
cis-2-butene
1-hexene no. 1
75
165
500
500
75
75
3.64
1-hexene no. 2
1-hexene no. 3a
100
1.9
500
2.5
75
25
overall
1-hexene
a Charcoal sampling; see text.
65% to the terminal C atom and 35% to C-2. Given these
numbers, the calculated branching ratios of the secondary and
the primary â-hydroxy nitrates are 0.013 and 0.019, respectively.
For the â-hydroxy nitrates produced from 1-butene, cis-2-
butene, and 1-hexene, we were also able to determine the
individual product yields. The initial conditions, the yield of
â-hydroxy nitrates from the precursor alkene, and the yields
determined from previous studies (where available) are sum-
marized in Table 1 for all alkenes studied. For alkenes other
than propene, we cannot reliably estimate the relative production
of the two â-hydroxyperoxy radicals. Thus, the total organic
nitrate yields in Table 1 then represent the number average
branching ratio for the two â-hydroxyalkylperoxy radical
precursors in the case of propene, 1-butene, and 1-hexene.
Including possible systematic errors, we estimate an absolute
uncertainty for each determination of (25% of the reported
yield.
Figure 4. Overall organic nitrate yields for n-alkanes and 1-alkenes
as a function of size.
The results of this study indicate that the â-hydroxy nitrate
yields from the reaction of â-hydroxy peroxy radicals with NO
increase as a function of the size of the alkene, similar to the
observations reported for alkylperoxy radicals2 (i.e., from OH
+ alkanes). A plot of the total hydroxy nitrate yield vs the
size of the corresponding hydrocarbon (including the yield from
isoprene7) is plotted in Figure 4, along with the calculated total
organic nitrate yields resulting from OH radical reaction with
the corresponding size n-alkane (calculated from information
in Carter and Atkinson2 and Kwok and Atkinson28), for comp-
arison. As shown in Figure 4, the yields of â-hydroxy nitrates
from the â-hydroxyperoxy radicals is significantly lower than
those from the corresponding unsubstituted peroxyalkyl radicals,
indicating that the presence of a â-hydroxy group has a
substantial negative effect on the yield of organic nitrates.

Hydroxy Nitrate Yields
J. Phys. Chem. A, Vol. 102, No. 45, 1998 8907
TABLE 2: Computational Study Results for D0(O-O) for Organic Peroxy Nitrite Intermediates
D0 (kJ/mol)
CH3CH2O-ONO
cis-perplanar
HOCH2CH2O-ONO
complex (p′p′-cis)
HOCH2CH2O-ONO
level of theory
cis-perplanar
MP2/6-31G(d)
B3LYP/6-31G(d)
G2MP2
67.8
45.2
71.1
56.0
34.7
68.6
61.5
43.9
78.2
Because much of the reactive hydrocarbon emitted into the
earth’s atmosphere is believed to be in the form of isoprene
and terpenes, i.e., alkenes, it is critically important to understand
the relationship between molecular structure and the organic
nitrate yields so that a predictive capability can be established.
To gain insight into the influence of the presence of an -OH
group on the carbon atom â to the peroxy group on the ultimate
organic nitrate yield, we conducted an ab initio molecular orbital
computational study. The reaction of organic peroxy radicals
with NO proceeds through an energy-rich peroxy nitrite
intermediate,29 which then rapidly either rearranges to form the
organic nitrate via reaction 9b or undergoes O-O bond scission,
i.e., reaction 9a:
Figure 5. Structure of the p′p′-cis hydrogen-bonded hydroxyethyl-
peroxy nitrite.
the expense of reaction 9b, accounting for the relatively smaller
observed â-hydroxy nitrate yields, as discussed for Figure 4.
We note that the rearrangement of the nitrite to a nitrate can
be considered to occur through a three-centered transition state.
To examine this, we consider HOONO as a model for the
rearrangement chemistry. The transition state for the rearrange-
ment of HOONO to HONO2 has been found to be ∼250 kJ
mol-1 higher in energy than HOONO.31-33 The O-O bond
dissociation energy in this species34,30 is ∼84 kJ mol-1. It is
very unlikely that transformation occurs via a three-centered
concerted mechanism in HOONO. If we assume as a first
approximation that the transition state for the rearrangement of
ROONO (where R ) CH3CH2 and CH2(OH)CH2) is compatible
with that for HOONO, even though we expect the geometry of
the three-centered transition state to be more hindered by the
substituents on the carbon chain, the O-O bond dissociation
values for the ROONO’s (as shown in Table 2) are well below
the isomerization barrier. The rearrangement for ROONO most
likely goes through O-O bond fission followed by RO + NO2
recombination.
The observed significant yields of organic nitrates from alkene
oxidation impacts on the expected role of organic nitrate for-
mation in the atmosphere. As discussed in Chen et al.,7 even
though the organic nitrate yield for OH reaction with isoprene
is relatively small at 4.4%, the impact of isoprene nitrate
formation is that an estimated 7% of NO emitted in the eastern
U.S. in the summer is removed from the atmosphere in the form
of the isoprene nitrates. The second major source of alkenes
to the atmosphere is the terpenes, which are emitted at an annual
rate of about 2/3 that of isoprene.35 We would therefore expect
the production of terpene-derived nitrates to have a similar, if
not larger, role as NOx sinks. The recently reported organic
nitrate yield of 17% from the OH reaction with R-pinene
(Nozie`re et al.36) is quite high compared to analogous â-hydroxy
nitrate yield measurements and indicates that our understanding
of the structural features that determine the magnitude of organic
nitrate yields may be incomplete. This reaction produces a
â-hydroxyperoxy nitrite intermediate, which, on the basis of
this work, would have been expected to have a smaller yield
than that reported.
•
RO2 + NO f ROONO*
(8)
ROONO* f RO• + NO2
f RONO2
(9a)
(9b)
That reaction 8 is not reversible is indicated by the fact that k8
is not pressure-dependent, while k9b/k9 increases with pressure.3
The competition between reactions 9a and 9b depends on the
distribution of internal energy among the available vibrational
modes in the peroxy nitrite, as well as the impact of any
structural features on the strength of the O-O bond. The latter
is conveniently studied through application of an ab initio
molecular orbital study. Here, we applied the MPL/6-31G(d)
and B3LYP/6-31G(d) levels of theory to a study of ethylperoxy
nitrite and 2-hydroxyethylperoxy nitrite, i.e., the ROONO
intermediates produced from OH radical oxidation of ethane
and ethene, respectively. Because of the observation of the
impact of the â-hydroxy group on the organic nitrate yields, it
was of particular interest to calculate the bond dissociation
energy for the peroxy nitrite O-O bond. To refine the
energetics for these systems, G2MP2 energies were calculated.
The results are shown in Table 2 for the three levels of theory
used in our study, i.e., MP2/6-31G(d), B3LYP/6-31G(d), and
G2MP2. For ethylperoxy nitrite, the most stable conformation
is the cis-perplanar species. The MP2 and G2MP2 results
indicate a consistent estimated D0(O-O) of 67.8-71.1 kJ/mol,
which is consistent with literature estimates for HO-ONO and
other RO-ONO species.30 For the hydroxyethylperoxy nitrite
species, we considered two stable conformations. There is a
cis-perplanar conformation, for which the D0(O-O) values are
comparable or somewhat smaller than for the simple ethylperoxy
nitrite. However, we find that there is also a p′p′-cis hydrogen-
bonded complex that, as shown from the data in Table 2, is
stabilized relative to the cis-perplanar conformation by ∼8-9
kJ/mol, relative to the non-hydrogen-bonded form. This
geometry facilitates an internal hydrogen bond from the hydroxy
group to one of the peroxy group oxygen atoms, as shown in
Figure 5. The H-bonding interaction then weakens the O-O
bond by ∼8-9 kJ/mol, i.e., in comparison to the D0(O-O) value
for the ethylperoxy nitrite species. The expected impact of this
weakened bond would be to increase the rate of reaction 9a at
Conclusions
Although the yields of â-hydroxy nitrates from alkenes were
found to be lower than those for the alkyl nitrates derived from
similar-size alkanes, â-hydroxy nitrates have a shorter atmo-

8908 J. Phys. Chem. A, Vol. 102, No. 45, 1998
O’Brien et al.
(13) Ridley, B. A.; Shetter, J. D.; Walega, J. G.; Madronich, S.; Elsworth,
C. M.; Grahek, F. e. J. Geophys. Res. 1990, 95 (D9), 13949.
(14) Shepson, P. B.; Anlauf, K. G.; Bottenheim, J. W.; Wiebe, H. A.;
Gao, N.; Muthuramu, K.; Mackay, G. I. Atmos. EnViron. 1993, 27A (5),
749.
(15) O’Brien, J. M.; Shepson, P. B.; Muthuramu, K.; Hao, C.; Niki, H.;
Taylor, R.; Roussel, P. J. Geophys. Res. 1995, 100 (D11), 22795.
(16) O’Brien, J. M.; Shepson, P. B.; Wu, Q.; Biesenthal, T.; Bottenheim,
J. W.; Wiebe, H. A.; Anlauf K. G.; Brickell, P. Atmos. EnViron. 1997, 31,
2059.
(17) Parrish, D. D.; Buhr, M. P.; Trainer, M.; Norton, R. B.; Shimshock,
J. P.; Fehsenfeld, F. C.; Anlauf, K. G.; Bottenheim, J. W.; Tang, Y. Z.;
Wiebe, H. A.; Roberts, J. M.; Tanner, R. L.; Newman, L.; Bowersox, V.
C.; Olszyna, K.; Bailey, E. M.; Rodgers, M. O.; Wang, T.; Berresheim, H.;
Roychowdhury, U. K.; Demerjian, K. L. J. Geophys. Res. 1993, 98, 2927.
(18) Bertman, S. B.; Roberts, J. M.; Parrish, D. D.; Buhr, M. P.; Goldan,
P. D.; Kuster, W. c.; Fehsenfeld, F. C.; Montzka, S. A.; Westberg, H. A. J.
Geophys. Res. 1995, 100, 22805.
spheric lifetime and their production may represent a more
efficient mechanism for removing NOx from the atmosphere.
This idea has recently been discussed in a modeling study by
Horowitz et al.,37 who find that a significant fraction of nitrogen
emitted in the U.S. is exported from North America in the form
of isoprene nitrates. Through the combination of the yields
determined in this study and field measurements of â-hydroxy
nitrates, computer modeling studies can better address the
question of the impact of organic nitrate formation on the
production of ozone and long-range transport of NOx. The
production of hydroxy nitrates could be an important process
for forest environments and in urban areas, where the yields
for the relatively larger biogenic or urban hydrocarbons (e.g.,
terpenes or aromatics) may be such that the production of
hydroxy nitrates represents an important mechanism for the
removal of atmospheric nitrogen. Thus, further work is clearly
necessary with regard to the mechanisms and yields for organic
nitrate formation from biogenic alkenes and aromatic hydro-
carbons to assess their importance as NOx removal processes
in urban and forested environments.
(19) Hao, C.; Shepson, P. B.; Drummond, J. W.; Muthuramu, K. Anal.
Chem. 1994, 66, 3737.
(20) Atlas, E.; Schauffler, S. EnViron. Sci. Technol. 1991, 25, 61.
(21) Noyes, W. A. J. Am. Chem Soc. 1933, 55, 3888.
(22) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M.; Johnson,
B. G.; Robb, M. A.; Cheeseman, J. R.; Keith, T. A.; Petersson, G. A.;
Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrewski, V.
G.; Ortiz, J. V.; Foresman, J. B.; Cioslowski, J.; Stefanov, B. B.;
Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen, W.;
Wong, M. W.; Andres, J. L.; Replogle, E. S.; Gomperts, R.; Martin, R. L.;
Fox, D. J.; Binkley, J. S.; Defrees, D. J.; Baker, J.; Stewart, J. J.; Head-
Gordon, M.; Gonzales, C.; Pople, J. A. Gaussian 94; Gaussian Inc.:
Pittsburgh, PA, 1995.
Acknowledgment. We thank the Natural Sciences and
Engineering Research Council of Canada and the National
Science Foundation (NSF9520374-ATM) for support of this
work. Many thanks are given to J. Bottenheim (Atmospheric
Environment Service) for the loan of equipment.
(23) Møller, C.; Plesset, M. S. Phys. ReV. 1934, 46, 618.
(24) Pople, J. A.; Binkley, J. S.; Seeger, R. Int. J. Quantum Chem. Symp.
1976, 10, 1.
(25) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B. 1988, 41, 785.
(26) Curtiss, L. A.; Raghavachavi, K.; Pople, J. A. J. Chem. Phys. 1993,
98, 1293.
(27) Atkinson, R.; Aschmann, S. M.; Carter, W. P. L.; Winer, A. M.;
Pitts, J. N., Jr. J. Phys. Chem. 1982, 86, 4563.
(28) Kwok, E.; Atkinson, R. Atmos. EnViron. 1995, 29, 1685.
(29) Maricq, M. M.; Szente, J. J. J. Phys. Chem. 1996, 100, 12374.
(30) Bach, R. D.; Ayala, P. Y.; Schlegel, H. B. J. Am. Chem. Soc. 1996,
118, 12758.
(31) Houk, K. N.; Condroski, K. R.; Pryor, W. A. J. Am. Chem. Soc.
1996, 118, 13002.
(32) Cameron, D. R.; Borrejo, A. M. P.; Bennett, B. M.; Thatcher, G.
R. J. Can. J. Chem. 1995, 73, 1627.
(33) Jursic, B. S.; Klasine, L.; Pecur, S.; Pryor, W. A. Nitric Oxide 1997,
1, 494.
(34) McGrath, M. P.; Rowland, F. S. J. Phys. Chem. 1994, 98, 1061.
(35) Guenther, A.; Hewitt, C. N.; Erickson, D.; Fall, R.; Geron, C.;
Graedel, T.; Harley, P.; Klinger, L.; Lerdau, M.; McKay, W. A.; Pierce,
T.; Scholes, B.; Steinbrecher, R.; Tallamraju, R.; Taylor, J.; Zimmerman,
P. J. Geophys. Res. 1995, 100, 8873.
(36) Nozie`re, B.; Barnes, I.; Becker, K. J. Geophys. Res., in press.
(37) Horowitz, L. W.; Liang, J.; Gardner, G. M.; Jacob, D. J. J. Geophys.
Res. 1998, 103, 13451.
References and Notes
(1) Chameides, W. L.; Fehsenfeld, F.; Rodgers, M. O.; Cardelino, C.;
Martinez, J.; Parrish, D.; Lonneman, W.; Lawson, D. R.; Rasmussen, R.
A.; Zimmerman, P.; Greenberg, J.; Middleton, P.; Wang, T. J. Geophys.
Res. 1992, 97, 6037.
(2) Carter, W. P. L.; Atkinson, R. J. Atmos. Chem. 1989, 8, 165.
(3) Atkinson, R. J. Phys. Chem. Ref. Data 1997, 26, 215.
(4) Muthuramu, K.; Shepson, P. B.; O’Brien, J. M. EnViron. Sci.
Technol. 1993, 27, 1117.
(5) Shepson, P. B.; Mackay, E.; Muthuramu, K. EnViron. Sci. Technol.
1996, 30, 3618.
(6) Shepson, P. B.; Edney, E. O.; Kleindienst, T. E.; Pittman, J. H.;
Namie, G. R.; Cupitt, L. T. EnViron. Sci. Technol. 1985, 19, 849.
(7) Chen, X.; Hulbert, D.; Shepson, P. B. J. Geophys. Res., in press.
(8) Tuazon, E. C.; Atkinson, R. Int. J. Chem. Kinet. 1990, 22, 1221.
(9) Atlas, E. Nature 1988, 331, 426.
(10) Atlas, E.; Ridley, B. A.; Hu¨bler, G.; Walega, J. G.; Carroll, M. A.;
Montzka, D. D.; Huebert, B. J.; Norton, R. B.; Grahek, F. E.; Schaufler, S.
J. Geophys. Res. 1992, 97, 10449.
(11) Buhr, M. P.; Parrish, D. D.; Norton, R. B.; Fehsenfeld, F. C.;
Sievers, R. E.; Roberts, J. M. J. Geophys. Res. 1990, 95 (D7), 9809.
(12) Flocke, F.; Volz-Thomas, A.; Kley, D. Atmos. EnViron. 1991, 25A,
1951.