S1
Supporting Information
Kinetics and
Products of
the R
eaction of the
First-
Generation
Isoprene
Hydroxy
Hydroperoxide (ISOPOOH) with OH
Jason M. St. Clair
†
, Jean C. Rivera-Rios
‡
, John D. Crounse
†
, Hasse
C.
Knap
§
, Kelvin H.
Bates
#
, Alex P.
Teng
†
, Solvejg
Jørgensen
§
, Henrik G. Kjaergaard
§
, Frank N. Keutsch
‡
ψ
,
Paul O. Wennberg
†
⊗
†
Division of Geological and Planetary Sciences, California Institute of Technology, 1200
E. California Blvd, Pasadena, CA 91125
‡
Department of Chemistry, University of
Wisconsin-Madison, 1101 University Avenue,
Madison, WI 53706
ψ
Paulson School of Engineering and Applied Sciences and Department of Chemistry
and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge MA 02138
§
Department of Chemistry, DK-
2100 Copenhagen Ø, University of Copenhagen,
Copenhagen, Denmark
#Division of Chemistry and Chemical Engineering, California Institute of Technology,
1200 E. California Blvd, Pasadena, CA 91125
S2
⊗
Division of Engineering and Applied Science, California Institute
of Technology, 1200
E. California Blvd, Pasadena, CA 91125
S1.0
CIMS Sensitivities
CIMS sensitivities to the oxidation products were determined
in multiple ways. Hydroxyacetone and glycolaldehyde are commercially available and
were quantified
gravimetrically and by Fourier Transform Infrared Spectroscopy (FT
-IR)
for CIMS calibration.
1
Uncalibrated compounds (glycolic acid and all products identified
by
m/z
) were assigned
a generic CIMS sensitivity of 2.5
×
10
-4
ncts
/pptv, and are
considered accurate to within a factor of 2.
Here,
normalized counts (ncts)
represent the
counts observed at the analyte
m/z
divided by the reagent ion counts. The reagent ion
counts
are
the sum of the signal at
m/z
= 86 (
13
CF
3
O
-
) and
m/z
= 104 (
13
CF
3
O
-
• H
2
O), as
well as
m/z
= 120 (
13
CF
3
O
-
• H
2
O
2
) for experiments with H
2
O
2
as the OH source.
The sensitivities for ISOPOOH and IEPOX were obtained by matching the output of a
box model to a laboratory isoprene + OH oxidation under low NO conditions. The
sensitivity is therefore dependent on the box model chemistry, including the yield of
ISOPOOH from isoprene (0.94) and the yield of IEPOX from ISOPOOH (0.8). The
ISOPOOH yield used was based on a 6% yield of methyl vinyl ketone and methacrolein
,
2
and the
IEPOX yield used was 80%, in general agreement with the sum of the non
-
IEPOX products observed by the CIMS in this study. ToF-CIMS sensitivities for
ISOPOOH and IEPOX were 1.6
×
10
-4
ncts/pptv and 1.9
×
10
-4
ncts/pptv, respectively. For
the TQ-CIMS, the MSMS
sensitivities were 5.1
×
10
-6
ncts/pptv and 3.9
×
10
-6
ncts/pptv for
ISOPOOH and IEPOX, respectively. The CIMS sensitivity to ISOPOOH was also
verified gravimetrically by completely evaporating a known mass of the pure compound
into a known volume of dry air
. For the
(4,3)-ISOPOOH, the sample evaporated
completely and gave a sensitivity of 1.6
×
10
-4
ncts/pptv. The
(1,2)-ISOPOOH gave a
sensitivity of 1.5
×
10
-4
ncts/pptv but with a slight residual mass, and 1.6
×
10
-4
ncts/pptv
was determined appropriate for both isomers.
S3
S2.0
Impurity Oxidation Products
The main impurities in the ISOPOOH samples, 2-
methyl-1-butene-3,4-diol for
(4,3)-ISOPOOH and 3-methyl-1-butene-3,4-diol for
(1,2)-
ISOPOOH, also react with OH to produce some of the same product masses as
ISOPOOH. To correct for the impurity oxidation products, both
methylbutanediols were
synthesized and each was oxidized by OH under similar conditions to the ISOPOOH
experiments. The ratio of the product formation to
methylbutanediol loss was then used
to remove the methylbutanediol products from the ISOPOOH experiment data.
S3.0
Ab Initio
Calculations
We
used the M06-2X/aug-cc-pVTZ method as implemented
in the Gaussian 09 program.
3
Frequency calculations were done at all
stationary points
with the same method to ensure that the equilibrium structures (reactants, reactive
complexes,
products) only have positive vibrational frequencies and the transition states
have one imaginary frequency. To ensure that the transition sta
te connects the reactive
complex and the product,
intrinsic reaction coordinate (IRC) calculations
4,5
were
performed and,
if needed,
the end product was optimized. None of the M06-2X/aug-cc-
pVTZ calculations have any significant spin contamination. Single
point energy
CCSD(T)-F12a/VDZ-F12 [F12] calculations
6,7
were performed
on the M06-2X/aug-cc-
pVTZ geometries. All the CCSD(T) calculations were carried out with the Molpro2012
program
8
suite using default convergence criteria. High T1
-diagnostic values were
observed
for
H-abstraction f
rom the OH group,
and
we have therefore used the M06-
2X/aug-cc-pVTZ energies
for Mesmer modeling. High T1-diagnostic values have
been
observed
previously
for H-shift from
OH groups.
9,10
For OH addition and H-abstraction
involving
-CH
2
and
>CH groups,
the M06-2X/aug-cc-pVTZ energies of
the
reactant
complex and the transition state are in good agreement with the CCSD(T)
-F12A/VDZ-
F12 energies. The M06-2X/aug-cc-pVTZ (and wb97-XD) method has also
previously
been found to calculate barrier heights similar to those obtained with the much more
computationally expensive CCSD(T)-F12A/VD2-F12 single point calculations on the
DFT geometry.
10
In the following we are therefore using the M06
-2X/aug-cc-pVTZ
energies for kinetic modeling.
S4
S3.1 The energetics of the
reaction between ISOPOOH and OH
We have assumed
that the association reaction between OH and ISOPOOH produces a reactive complex
(ISOPOOH-OH). The reactive complex can hereafter overcome the transition state and
produce the different product complexes and products.
OH + ISOPOOH
à
ISOPOOH-OH
à
Products
In Figures S1 and S2 the different reaction pathways for (1,2)-ISOPOOH and (4,3)-
ISOPOOH are shown, respectively, and the energetics of the reaction pathways are given
in Tables S1 and S2. The reactant complexes for each of the individual reaction path are
different.
S5
Figure S1.
The different reaction pathways for the reaction between (1,2)
-ISOPOOH
and OH radical.
S6
Figure S2.
The different reaction pathways for the reaction between (4,3)
-ISOPOOH
and OH radical.
S7
Table S1.
The relative energies (kcal/mol) for the reaction between the (1,2)
-ISOPOOH
molecule and the OH radical with the M06
-2X/aug-cc-pVTZ method and the F12//M06-
2X/aug-cc-pVTZ. The values in () are the F12//M06-2X/aug-cc-pVTZ values. The
energies are corrected with zero point vibrational energies.
OH
-CH
2
-
H-OO
Add1
Add2
(1,2)-ISOPOOH+OH
0.0
0.0
0.0
0.0
0.0
Reactive Complex
-8.9
(-8.3)
-7.3
(-6.1)
-5.0
(-3.7)
-6.2
(-6.1)
-7.8
(-6.2)
Transition State
-2.2
(-1.0
a
)
-4.0
(-3.5)
-3.8
(-3.3)
-5.3
(-5.2)
-5.6
(-5.4)
Product Complex
-21.8
(-20.9)
-34.0
(-33.0)
-40.8
(-40.2)
-
-
Product
-13.8
(-8.7)
-24.2
(-23.5)
-34.7
(-34.4)
-34.4
(-31.1)
-33.4
(-30.0)
a
This calculation has a T1 diagnostic value of 0.078
Table S2.
The relative energies (kcal/mol) for the reaction between (4,3)
-ISOPOOH and
OH with the M06-2X/aug-cc-pVTZ method and the F12//M06-2X/aug-cc-pVTZ. The
values in () are the F12//M06-2X/aug-cc-pVTZ values.. The energies are corrected with
zero point vibrational energies.
OH
-CH
2
-
-CH-
H-OO
Add1
Add2
(4,3)-ISOPOOH+OH
0.0
0.0
0.0
0.0
0.0
0.0
Reactive Complex
-6.2
(-5.3)
-6.8
(-6.2)
-6.4
(-4.9)
-5.7
(-4.4)
-7.7
(-6.5)
-5.8
(-4.3)
Transition State
-0.4
(25.6
a
)
-1.7
(-1.3)
-4.8
(-4.5)
-2.8
(-1.5
b
)
-7.7
(-7.0)
-2.7
(-5.1)
Product Complex
-19.4
(-18.1)
-30.6
(-29.2)
-43.0
(-41.3)
-36.0
(-35.1)
-
-
Product
-10.8
(-9.7)
-23.2
(-22.5)
-33.9
(-34.2)
-33.4
(-33.2)
-34.9
(-31.7)
-31.2
(-28.7)
a
This calculation has a T1 diagnostic value of 0.116
b
This calculation has a T1 diagnostic value of 0.058
S8
S3.2
The kinetics of the
reaction between ISOPOOH and OH
The kinetic calculations
are carried out using the master equation solver for multi energy well reaction, MESMER
program.
11,12
The general reaction scheme is shown in Figure S3.
Figure S3.
The reaction scheme as used in the MESMER model (Only an illustration, not
the energetically correct picture of the reactions). The ISOPOOH
-OH complexes are
different for each of the reaction pathways even though they are given with the same
energy at this figure.
In our Mesmer modeling the Lennard-Jones (L-J) parameters of the bath gas were chosen
to be a nitrogen gas resembling the atmospheric gas (
σ
(N
2
) = 3.919 Å,
ε
/k
b
(N
2
) = 91.85
K)
whereas the reactive complex (ISOPOOH
-OH) is modeled with the L-J parameters of
methylcyclohexane (
σ
(methylcyclohexane) = 7.045 Å,
ε
/k
b
(methylcyclohexane) =
379.95 K)
.
13
The average collisional activation/deactivation energy transfer of all the
molecules is set to 200 cm
-1
per collision and the grain size of each grain is 50 cm
-1
. The
span of the energy grains is set to 30
k
T above the highest stationary point. We have used
a pressure of 745 Torr and a temperature of 298 K for all the calculations, similar to the
experimental conditions.
ISOPOOH + OH
ISOPOOH
-
OH
complex
TS
TS
TS
Abstraction
trans
-
Add1
cis
-
Add1
Add2
trans
-
IEPOX
cis
-
IEPOX
S9
We have preformed a sensitivity test of Mesmer input parameters. In our sensitivity test
we used three collisional activation/deactivation energies of 50, 100 and 200 cm
-1
and
two different grain sizes of 25 and 50 cm
-1
. We did not observe
any significant changes in
the reaction rate constants (only changes of a few percent). We have also tested the
system with different sizes of grain span, e.g., 10
k
T, 20
k
T, 30
k
T, 40
k
T and 50
k
T. If a
grain span of 30
k
T or higher
is used, the reaction
rate constants do
not change. We have
therefore used a grain size of 30
k
T.
The reaction rate constants are sensitive to the choice of the Arrhenius pre
-exponential
factor (A). Each reaction pathway is a separate Mesmer calculation (See Figure S
4 and
S5
for the individual reaction
pathways)
– we have not coupled
between the reactions in
the fitting of the Arrhenius pre-exponential factor (A). We treat the pre-exponential factor
as temperature independent and it is varied between 1.0
×
10
-12
and 2.0
×
10
-10
cm
3
molecule
-1
s
-1
. We use nine different Arrhenius pre-exponential factors to calculate the
rates. Three of the
factors
are from the three reactions of n-butane, 3-methyl-3-butene-1-
ol and 1-butene with OH.
14-
16
The total reaction rate constants (OH +ISOP
OOH
→
Products) of the (1,2)-ISOPOOH and (4,3)-ISOPOOH systems are shown in Table S3
and Table S4, respectively.
S3.3 (1,2)-ISOPOOH
For the (1,2)-ISOPOOH + OH reactions,
the absolute rate
constants of all the different reaction pathways increase with an
increase
in
the Arrhenius
pre-exponential factor,
and
the relative yields (in %) of the reaction pathways also change.
The yield of the two addition reactions increased more compared to yield of the three
abstraction reaction pathways with increasing Arrhenius pre-exponential factor. The rate
constant is sensitive to the Arrhenius pre-exponential factor since the energy of the
transition state is below the energy of the individual reactants. The rate constant for each
reaction path is therefore almost identical to the Arrhenius pre-exponential factor.
With
an
Arrhenius pre-exponential factor
of
1
×
10
-11
cm
3
molecule
-1
s
-1
for the OH
abstraction reactions and 6
×
10
-11
cm
3
molecule
-1
s
-1
for the addition reactions (see Mix
S10
column, Table S3),
the yield of the (1,2)-ISOPOOH + OH reactions
is
OH (1.1),
-CH
2
-
(7.0), H-OO (7.9), Add1 (53.7),
and Add2 (30.2). The rate constant for abstraction is
1.2
×
10
-11
cm
3
molecule
-1
s
-1
and the rate constant for addition is 6.2
×
10
-11
cm
3
molecule
-1
s
-1
. The sum of the OH addition
and OH abstraction rate constants are 7.4
×
10
-11
cm
3
molecule
-1
s
-1
, and was constrained to mimic the experimentally determined rate.
S3.4 (4,3)-ISOPOOH
With an
Arrhenius pre-exponential factor
of
5x10
-12
cm
3
molecule
-
1
s
-1
for the OH abstraction reactions and 1.5x10
-10
cm
3
molecule
-1
s
-1
for the addition
reactions (see Mix column, Table S4)
, the yield of the (4,3)-ISOPOOH + OH reactions
is
OH (0.1),
-CH
2
- (0.5),
-CH-
(4.0), H-OO (2.3), Add1 (89.0), and Add2 (4.1). The rate
constant for abstraction is 7.2
×
10
-12
cm
3
molecule
-1
s
-1
and the rate constant for addition is
9.7
×
10
-11
cm
3
molecule
-1
s
-1
. The sum of these, 1.1
×
10
-10
cm
3
molecule
-1
s
-1
, was
constrained to mimic the experimentally determined rate.
S
11
Table S3.
The reaction rate constants at 298K (in cm
3
molecules
-1
s
-1
) for the reaction b
etween the (1,2)-ISOPOOH molecule
and the
OH radical with the M06-2X/aug-cc-pVTZ method. All the reaction rates are without tunneling correction. In () are the yields in
percent. The ratios are calculated as
Γ
i
=k
i
/k
tot
*100%, where k
tot
=
Σ
k
i
Absolute rate
(yield
, %
)
A(1
·10
-12
)
a
A(2
·10
-12
)
A(5
·10
-12
)
b
A(1
·10
-11
)
A(3
·10
-11
)
c
A(6
·10
-11
)
A(1
·10
-10
)
A(1.5
·10
-10
)
A(2
·10
-10
)
Mix
d
OH
3.3·10
-13
(8.3)
4.7·10
-13
(6.4)
6.8·10
-13
(4.2)
8.2·10
-13
(3.0)
1.0·10
-12
(1.7)
1.1·10
-12
(1.2)
1.2·10
-12
(1.0)
1.2·10
-12
(0.8)
1.2·10
-12
(0.8)
8.2·
10
-13
(1.
1)
-CH
2
-
8.6·10
-13
(21.8)
1.6·10
-12
(21.4)
3.2·10
-12
(20.2)
5.2·10
-12
(18.7)
9.2·10
-12
(15.5)
1.2·10
-11
(13.5)
1.4·10
-11
(12.1)
1.6·10
-11
(11.0)
1.7·10
-11
(10.4)
5.2·10
-12
(7.0)
H-
OO
9.0·10
-13
(22.8)
1.7·10
-12
(22.8)
3.6·10
-12
(22.3)
5.8·10
-12
(21.2)
1.1·10
-11
(18.3)
1.4·10
-11
(16.1)
1.7·10
-11
(14.3)
1.9·10
-11
(13.2)
2.0·10
-11
(12.4)
5.8·
10
-12
(7.9)
Add1 (C1)
9.8·10
-13
(24.9)
1.9·10
-12
(26.3)
4.7·10
-12
(29.3)
9.0·10
-12
(32.6)
2.3·10
-11
(39.4)
4.0·10
-11
(44.3)
5.6·10
-11
(48.0)
7.2·10
-11
(50.6)
8.5·10
-11
(52.4)
4.0·10
-11
(53.7)
Add2 (C2)
8.8·10
-13
(22.3)
1.7·10
-12
(23.0)
3.8·10
-12
(24.0)
6.8·10
-12
(24.6)
1.5·10
-11
(25.1)
2.2·10
-11
(24.9)
2.9·10
-11
(24.6)
3.5·10
-11
(24.3)
3.9·10
-11
(24.0)
2.2·10
-11
(30.2)
a
P re-exponential factor from an OH reaction with n
-butane (Abstraction) [3].
b
Pre
-exponential factor from the reaction of OH with 3
-methyl
-3-
buten-1-
ol (Addition and Abstraction)[4].
c
Pre
-exponential factor from OH and 1
-butene (Addition)[5].
d
In the M
ix column, the addition
and
the abstraction reactions
use an Arrhenius value
of 6·
10
-11
and
1· 10
-11
cm
3
molecule
-1
s
-1
, respectively.
S
12
Table S4.
The absolute reaction rates at 298K in units of cm
3
molecules
-1
s
-1
for the OH radical reaction with the (4,3)-ISOPOOH
molecule with the M06-2X/aug-cc-pVTZ method. All the reaction rates are without tunneling correction. In () are the ratios of the
different OH and (4,3)-ISOPOOH reactions shown. The ratios are calculated as
Γ
i
=k
i
/k
tot
*100%, where k
tot
=
Σ
k
i
Absolute
rate
(yield
, %
)
A(1·10
-12
)
a
A(2·10
-12
)
A(5·10
-12
)
b
A(1·10
-11
)
A(3·10
-11
)
c
A(6·10
-11
)
A(1·10
-10
)
A(1.5·10
-10
)
A(2·10
-10
)
Mix
d
OH
7.1·10
-14
(1.2)
7.7·10
-14
(1.2)
8.1·10
-14
(0.6)
8.2·10
-14
(0.4)
8.4·10
-14
(0.2)
8.5·10
-14
(0.1)
8.5·10
-14
(0.1)
8.5·10
-14
(0.1)
8.5·10
-14
(0.0)
8.1·
10
-14
(0.1)
-CH
2
-
3.1·10
-13
(6.8)
4.2·10
-13
(6.8)
5.5·10
-13
(4.4)
6.3·10
-13
(3.0)
7.2·10
-13
(1.6)
7.7·10
-13
(1.0)
7.9·10
-13
(0.7)
8.0·10
-13
(0.6)
8.1·10
-13
(0.5)
5.5·
10
-13
(0.
5)
-CH
-
9.3·10
-13
(29.3)
1.8·10
-12
(29.3)
4.1·10
-12
(33.3)
7.4·10
-12
(35.7)
1.7·10
-11
(36.3)
2.5·10
-11
(33.6)
3.2·10
-11
(30.3)
3.9·10
-11
(27.2)
4.4·10
-11
(24.9)
4.1· 10
-12
(4.0)
H-
OO
7.9·10
-13
(21.8)
1.3·10
-12
(21.8)
2.4·10
-12
(19.1)
3.3·10
-12
(15.9)
4.8·10
-12
(10.5)
5.5·10
-12
(7.4)
6.0·10
-12
(5.6)
6.3·10
-12
(4.4)
6.5·10
-12
(3.7)
2.4·
10
-12
(2.3)
Add1
(C1)
6.9·10
-13
(22.3)
1.4·10
-12
(22.3)
3.4·10
-12
(27.4)
6.8·10
-12
(32.7)
2.0·10
-11
(44.0)
3.9·10
-11
(52.7)
6.4·10
-11
(59.4)
9.2·10
-11
(64.7)
1.2·10
-10
(68.3)
9.2·10
-11
(89.0)
Add2
(C2)
7.0·10
-13
(18.5)
1.1·10
-12
(18.5)
1.9·10
-12
(15.2)
2.5·10
-12
(12.1)
3.4·10
-12
(7.5)
3.8·10
-12
(5.2)
4.1·10
-12
(3.8)
4.3·10
-12
(3.0)
4.4·10
-12
(2.5)
4.3·10
-12
(4.
1)
a
P re-exponential factor from an OH reaction with n
-butane (Abstraction) [3]
b
Pre
-exponential factor from the reaction of OH with 3
-methyl
-3-
buten-1-
ol (Addition and Abstraction)[4].
c
Pre
-exponential factor from OH and 1
-butene (Addition) [5].
d
In the Mix column, the addition
and the abstraction reactions use an Arrhenius valu
e of
1.5·
10
-10
and
5·
10
-12
cm
3
molecule
-1
s
-1
, respectively.
S13
S3.5
IEPOX production
The formation of
cis
-
β
-IEPOX (
cis
-C
1
C
2
), the product of the
addition to C
1
in
(1,2)-ISOPOOH,
has a rate constant (the “energetically cold” reaction
rate constant) which is three times faster than the rate constant for the formation of
trans
-
β
-IEPOX (trans-C
1
C
2
). The
trans
-
β
-IEPOX (trans-C
4
C
3
) rate is faster than the
cis
-
β
-
IEPOX (
cis
-C
4
C
3
) production rate in the (4,3)-ISOPOOH+OH reaction. The
trans
-C
4
C
3
rate constant is fastest because of a lower transition state barrier. The differences between
the reaction rate constants of the
cis/trans
-C
1
C
2
isomers are due to changes in the
vibrational partition functions (Table S5).
We have used the bimolecular reaction rate constant obtained by Park et al.
7
, 2.3
×
10
-12
cm
3
molecule
-1
s
-1
for the reaction between molecular oxygen and OH
-isoprene, to
represent the bimolecular reaction between our OH addition p
roducts and molecular
oxygen. With the Park et al. reaction rate constant and a molecular oxygen concentration
of 5.2
×
10
18
molecule cm
-3
the pseudo-first order reaction rate becomes 1.2
×
10
7
s
-1
.
The "cold" reaction rate constants are estimated using transition state theory including the
quantum tunneling given by
k
!"!
=
k
!
T
h
Q
!"
Q
!
exp
−
∆
E
k
!
T
where
Q
!
and
Q
!"
are the partition functions for the reactant, R, and the transition state,
TS, respectively
.
18
The rigid rotor and harmonic oscillator approximations have been used
to calculate the partition functions. The energy
∆
E
is the energy difference between the
transition state and the reactant. The constants
, h and k
B
, are the Planck constant and the
Boltzmann constant, respectively. Tunneling was done with the Eckart approach
.
19
The "cold" TST reaction rate constants are all much slower than the estimated pseudo
-
first order reaction rate constant of the OH
-addition
ISOPOOH products and molecular
oxygen. With this reaction rate constant the bimolecular reaction dominates over the
cis/trans
-
β
-IEPOX production at atmospheric pressures.
S14
Table S5.
The energy barriers, transition state theory (TST) reaction rate constants and
the Eckart-corrected TST reaction rate constants for the production of IEPOX. The
energies are calculated with the M06
-2X/aug-cc-pVTZ method.
Species
Δ
E
forward /
(kcal/mol)
k
TST
/ (
s
-1
)
k
TST
·
κ
Eckart
/
(
s
-1
)
cis
-C
1
C
2
12.8
3.7
×
10
3
9.2
×
10
3
trans
-C
1
C
2
12.8
1.1
×
10
3
2.8
×
10
3
cis
-C
4
C
3
12.4
2.1
×
10
3
4.9
×
10
3
trans
-C
4
C
3
10.6
3.5
×
10
4
7.4
×
10
4
S3.6 Mesmer Modeling
Our MESMER models have all the ISOPOOH+OH reactions
along with the
cis/trans
-
β
-IEPOX production reactions that occur following the OH
addition to the outer carbon. All the
reactions are shown in Figure S4
and Figure S5
for
the
(1,2)-ISOPOOH and
(4,3)-ISOPOOH molecules, respectively. We have used a grain
size of 50 cm
-1
and a grain span in the model of 30 kT (above the ISOPOOH+OH energy
stationary point). We used a collisional activation/deactivation energy of 200 cm
-1
per
bath gas (N
2
) collision, a temperature of 298.15 K, a pressure of 745 Torr and an OH
concentration of 10
6
molecules cm
-3
.
(1,2)-ISOPOOH+OH
The yields of each component are shown on Figure S4. The total
for the compounds’
yields shown in bold add to 100%. Our model suggests that only a
minor amount of the ISOPOOH-OH molecules are stabilized in the ISO
POOH-OH well.
For the (1,2)-ISOPOOH+OH reaction in Figure S4, we observe that the two addition
reactions (Add1 and Add2) dominate over all the OH abstraction reactions. All OH
abstraction reactions have yields that are lower than 7%. The OH addition to the
inner
carbon of the double bond has a yield of 29% of the total yield. After the inner OH
addition, molecular oxygen adds and a hydroperoxydiol peroxy radical is produced.
S15
Figure S4.
The reactions for the (1,2)-ISOPOOH with OH.
S16
The
H-shift
between the hydroperoxy hydrogen and the peroxy radical is calculated to be
very fast (~10
4
s
-1
) – much faster than the bimolecular chemistry
– so
an equilibrium
distribution between the two peroxy radicals will result. The calculations suggest that the
peroxy radical on C
2
will be favored.
The yield of the OH addition to the outer carbon is 56%. After the OH addition, the
molecule can either produce
cis/trans
-
β
-IEPOX or a peroxy
hydroperoxydiol molecule.
Our model shows that the excess energy is high
enough to overcome the energy barriers
and to produce a high yield of
β
-IEPOX molecules. The 56% of OH addition to the outer
carbon will divide into a production of a total yield of 19%
trans
-
β
-IEPOX, 27%
cis
-
β
-
IEPOX molecule and 10% will add O
2
yielding
a hydroperoxydiol peroxy radical. H
-shift
between the hydroperoxy hydrogen and the peroxy radical is also calculated to be very
fast (~10
4
s
-1
) – much faster than the bimolecular chemistry and so, an equilibrium
distribution between the two peroxy radicals
will result.
(4,3)-ISOPOOH + OH
The calculated yields of each component are shown on the
Figure S5. The total for the yields shown in bold add to 100%. OH addition to the outer
carbon in the double bond dominates with a yield of 95% of the total yield.
The yield of
the OH abstraction reaction of the hydrogen
α
to the hydroperoxy group is around 3%,
and all other reactions have production yields around 1% or lower. Of the 95% yield
added to the outer carbon around 40% will produce the
cis
-
β
-IEPOX, 47% produce
trans
-
β
-IEPOX and around 8%
will produce the hydroxyperoxydiol peroxy radical. The yield
of
cis/trans
-
β
-IEPOX is much higher for (4,3)-ISOPOOH+OH compared to (1,2)-
ISOPOOH+OH.
S17
Figure S5.
The reactions for the (4,3)-ISOPOOH with OH.
S18
S3.7
Further decomposition after the inner OH addition to the
(1,2)-ISOPOOH
molecule
Following addition of OH to the
(1,2)-ISOPOOH via add2, we expect O
2
to add
(C4OO) rather than formation of a 4 member epoxide-like compound.
After O
2
addition,
we find a rapid H-shift from the hydroperoxide group to the ROO (C2OO). A reaction
scheme is shown in Figure S6. We have
looked at the (R,R)-enantiomer
of the molecule
and performed preliminary calculations with the
M06
-2X/aug
-cc-
pVTZ
method. The
calculated H-shift barrier height for this reaction is found to be
9.3
kcal/mol. The product
is 0.4
kcal/mol lower than the reactant. The attachment of molecular oxygen releases an
energy of
34.4
kcal/mol compared to
the
(1,2)-ISOPOOH-OH added product (inner
addition),
and
the energy difference between the
(1,2)-ISOPOOH+OH+O
2
and the
molecule with the oxygen attached (reactant) is
63.8
kcal/mol. The "cold" TST reaction
rate constants,
including the Eckart tunneling correction
, are
5.6
×
10
6
s
-1
and
5.8
×
10
6
s
-1
for the forward and backward H-shift reactions, respectively.
The second H-shift reaction
would likely take the terminal hydrogen with the OOH group,
and lead to loss of OH. It has a barrier height of
23.1
kcal/mol and a TST Eckart-
corrected reaction rate constant of 1.2
×
10
-4
s
-1
. The energy of the final
aldehyde+OH is
almost
50.4
kcal/mol lower in energy than the transition state.
The energetics are shown
in Table S6.
S19
Table S6.
The energetics (in kcal/mol) of the two H
-shift reactions after the inner OH
addition (+O
2
) to the (1,2)-ISOPOOH molecule calculated with the
M06
-2X/aug
-cc-
pVTZ method
.
Species
Δ
E+ZPVE / kcal/mol
(1,2)-ISOPOOH+OH+O
2
0.0
C4OO
-63.8
TS
-53.0
C2OO
-64.2
TS
-41.1
Aldehyde+OH
-91.5
S20
Figure S6.
The two possible H-shift reactions after the internal OH addition (+O
2
) in the
(1,2)-ISOPOOH molecule.
S21
S4.0 GEOS
-CHEM Calculations
The chemical mechanisms for the ‘Standard’ and ‘Old’ GEOS
-Chem runs were identical
except for the differences included in
Table S7. The complete ‘Standard’ mechanism can
be obtained at http://wiki.seas.harvard.edu/geos
-chem/index.php/New_isoprene_scheme.
Table S7.
Differences between the ‘Standard’ and ‘Old’ GEOS-Chem mechanisms.
‘Standard’
‘Old’
HO
2
+RO
2
rate
coefficient
2.91
×
10
-13
×
exp(1300/T)
×
[1-
exp(-0.245
×
n]
7.4
×
10
-13
×
exp(700/T)
H-abstraction rate
coefficient
4.75
×
10
-12
×
exp(200/T)
3.8
×
10
-12
×
exp(200/T)
H-abstraction yields
0.387 ISOPOO +
0.613 OH + 0.613
HC5
0.70 ISOPOO +
0.300 HC5 + 0.300
OH
The ‘Recommended’ simulation run in GEOS-Chem included an increased ISOPOOH
yield of 94% from the reaction of HO
2
with ISOPOO, as well as individually speciated
ISOPOOH and IEPOX isomers. Listed below are the rates and products of individual
reactions edited and added to the GEOS
-Chem mechanism in the ‘
Recommended’
simulation to account for the isomers of ISOPOOH and
IEPOX. In the GEOS-Chem
mechanism, ISOPOOH is referred to as RIP; RIPA, RIPB, and RIPD refer to (1,2), (4,3),
and delta
(1,4 and 4,1) ISOPOOH respectively, while IEPOXA, IEPOXB, and IEPOXD
refer to
trans-
β
,
cis-
β
, and delta
IEPOX respectively. Temperature
dependencies of rate
constants were kept from the ‘standard’ GEOS
-Chem mechanism.
RIO2 + HO2
à
0.628 RIPA + 0.272 RIPB + 0.037 RIPD + 0.063 (OH + CH2O + HO2)
+ 0.038 MVK + 0.025 MACR;
k
= 2.06e-13*exp(1300/T)
RIPA + OH
à
0.750 RIO2 + 0.250 HC5 + 0.125 (OH + H2O);
k
= 6.13e-12*exp(200/T)
S22
RIPA + OH
à
0.850 OH + 0.578 IEPOXA + 0.272 IEPOXB + 0.150 HC5OO;
k
=
1.70e-11*exp(390/T)
RIPB + OH
à
0.480 RIO2 + 0.520 HC5 + 0.26 (OH + H2O);
k
= 4.14e-12*exp(200/T)
RIPB + OH
à
1.000 OH + 0.680 IEPOXA + 0.320 IEPOXB;
k
= 2.97e-11*exp(390/T)
RIPD + OH
à
0.250 RIO2 + 0.750 HC5 + 0.375 (OH + H2O);
k
= 5.11e-12*exp(200/T)
RIPD + OH
à
0.500 OH + 0.500 IEPOXD + 0.500 HC5OO;
k
= 2.92e-11*exp(390/T)
IEPOXA + OH
à
IEPOXOO;
k
= 3.73e-11*exp(-400/T)
IEPOXB + OH
à
IEPOXOO;
k
= 5.79e-11*exp(-400/T)
IEPOXD + OH
à
IEPOXOO;
k
= 3.20e-11*exp(-400/T)
Other reactions involving RIP and IEPOX in the original GEOS
-Chem mechanism,
including deposition and photolysis, were simply updated to apply to each individual
isomer of the two compounds.
References:
1.
St.
Clair, J. M.;
Spencer, K. M.;
Beaver M. R.; Crounse, J. D.; Paulot, F.;
Wennberg,
P. O., Quantification of
Hydroxyacetone and
Glycolaldehyde
Using
Chemical
Ionization Mass
Spectrometry.
Atmos. Chem. Phys
.
2014
, 14, 4251-4262.
2.
Liu, Y. J.; Herdlinger-Blatt, I.; McKinney, K. A.; Martin, S. T., Production of
Methyl
Vinyl
Ketone and
Methacrolein via the
Hydroperoxyl
Pathway of
Isoprene
Oxidation.
Atmos. Chem. Phys.
2013,
13
(11), 5715-5730.
3.
Frisch, M.; Trucks, G.; Schlegel, H. B.; Scuseria, G.; Robb, M.; Cheeseman, J.;
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Gaussian.
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2009
.
4.
Gonzalez, C.; Schlegel, H. B., An
Improved
Algorithm for
Reaction-path
Following.
J. Chem. Phys.
1989,
90
, 2154-2161.
5.
Gonzalez, C.; Schlegel, H. B., Reaction-path
Following in
Mass
-weighted
Internal
Coordinates.
J. Phys. Chem.
1990,
94
, 5523-5527.
6.
Adler, T. B.; Knizia, G.; Werner, H.-J., A
Simple and
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Approximation.
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7.
Peterson, K. A.; Adler, T. B.; Werner, H.-J., Systematically
Convergent
Basis
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for
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Correlated
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