Transcript Acetone and Hydroperoxyl Radical Equilibrium Certainly Fascinating, But Is It Important To You? Fred Grieman, Aaron Noell, Stan Sander, Mitchio Okumura Funding: NASA Upper Atmospheric Research.

Acetone and Hydroperoxyl
Radical Equilibrium
Certainly Fascinating, But Is It
Important To You?
Fred Grieman, Aaron Noell, Stan Sander, Mitchio Okumura
Funding:
NASA Upper Atmospheric Research Program
NASA Senior Post-Doctoral Fellowship
NASA Summer Faculty Research Fellow Program
Importance to you?
HO2/OH Atmospheric Chemistry
Laboratory Study of and Atmospheric Observation of HOx Radicals
For example: Photochemical Ozone Production
Simplified Tropospheric Chemistry
Volatile Organic Compounds
Oxygenated Volatile
Organic Compounds
Understanding Atmospheric Chemistry
Overall Picture
HO2 + Acetone  HO2Acetone  (CH3)2C(OH)OO?
Acetone in the Upper Atmosphere
• One of main OVOCs in the Upper Troposphere (UT)
• Key source of OH and HO2 (HOx) from photolysis
• Primary loss pathways in Upper Troposphere: Photolysis, Reaction with OH
• Recent experiments by Blitz, Orr-Ewing, Heard, Pilling
suggest much lower photolysis yields at low T
An alternate oxidation pathway in the atmosphere?
Possible Reaction with HO2?
•
•
•
Hydrogen radicals in Upper Troposphere: HOx = OH, HO2
In the atmosphere, [HO2] >> [OH]
HO2 is known to react rapidly with formaldehyde at room temperature
So, YES!!! Determination of Acetone/Hydroperoxyl
Radical Equilibrium IS Important to YOU!
Literature?
Int. J. Chem. Kinet. 32, 573 (2000).
REACTANTS
ADDUCT
HO2 + Acetone  HO2Acetone
 (CH3)2C(OH)OO?
MOLECULAR
COMPLEX
PEROXY RADICAL
HO(iPr)OO
COMPUTED STATIONARY POINTS
B3LYP/cc-pVTZ Geometries
G2Mc/DFT Energies
Atmospheric Loss Process
1. HO2 + Acetone are in equilibrium with peroxy
(H-bonded molecular complex is pre-equilibrium config)
HO2 + CH3C(O)CH3 → HOC(CH3)2OO
k(200K) = 6.9 10-12 cm3 s-1
Kc(210K) = 6.0  10-13 cm3
2. Peroxy radical reacts with HO2 or NO, leading to loss of HO2
(then important to include in HO2 / OH budget)
3. Acetone sink: If Herman’s et al. calculation correct,
HO2 removal on par with photolysis
& greater than from OH
Abstraction
Higher Barrier
– NO REACTION!
Addition
Does this rxn occur at relevant atmospheric T?
k+
HO2 + CH3C(O)CH3 ⇌
k- HOC(CH3)2OO
k+
k-
Kc(T)
4.50E-13
1.06E-12
2.20E-12
4.04E-12
1.98E+04
4.58E+02
1.89E+01
1.33E+00
2.27E-17
2.32E-15
1.17E-13
3.05E-12
Because k- is so large, Keq is the quantity that determines effective rate of removal
How?? Experimental Determination via
Infrared Kinetics Spectroscopy (IRKS)
Infrared Kinetic Spectroscopy Apparatus
NIR
6.8 MHz
current modulator
{2ν(OH)}
computer
diode
laser
low pass
filter
λ = 220 nm (near HO2 max)
monochromator
2x/
phase shifter
UV
detector
D2 lamp
Excimer laser
308 nm
FM signal
PD
demodulated
signal
Herriott cell
exit
exit
gas entrance
T-controlled
FLOW CELL
Cl2 + hν → 2 Cl
Cl + CH3OH → CH2OH + HCl
CH2OH + O2 → HO2 + CH2O
Herriot Cell Mirror
FM Detection of HO2 NIR Lines by Diode Laser
5x10-7 Hz or 2. 5x10-10 cm-1Hz
HO2 Detection Limit (6636 cm-1, 295K, 100 Torr):
1.0 x 1010 cm-3
3 x 1011 cm-3
1 Hz
10kHz, 1 shot
HO2 line
6625.80 cm-1
1.5
HO2 Signal
(microvolt)
InGaAs/InP single-mode DFB Diode Lasers
1.4 and 1.5 m fabricated at JPL,
Selectivity for HO2
Detection of single rotational lines
Wavelength Modulation
2f detection at 7 MHz modulation
Near shot-noise limited detection
Herriott Cell
30 passes, Leff = 2000 cm
Sensitivity (Minimum detectable absorption)
1.0
0.5
0.0
-40
-30
-20
-10
-0.5
0
10
20
-1.0
Relative Frequency (milli-cm -1)
30
40
Association Reaction
MOLECULAR
COMPLEX
Measuring [HO2] decay upon adding Acetone
HO2 + (CH3)2CO ⇄ (CH3)2CO---HO2
↓
isomerization
← (CH3)2CO---H
(CH3)2COH
Does not occur at room T, but may at lower T
†
Measure with increasing [Acetone]
O▬O
O▬O
2-hydroxyisopropylperoxy
(2-HIPP)
Preliminary Result:
HO2 NIR Decay Curves at Varying [Acetone]
T = 221 K
T = 297 K
0.16
0.14
HO2 Absorbance
No HO2 + Acetone rxn !!!
IR02t [Ace] = 0.0e15
2.18
MustIR03t
consider
all chemistry
IR04t 4.06
IR05t 5.48
Cl + Acetone

IR06t 5.41
IR07t 7.09
HCl + CH3C(O)CH2
IR08t 9.93
IR09t 12.8
IR10t 17.5
Decreases
HO2 made
IR11t 20.5
Slows at Low T
0.12
0.10
Dramatic
decrease
IR05t [Ace] = 0
in
IR06t[HO
2.24e15 2] at lower T
IR09t
& 2.98e15
same [Acetone]
IR10t 3.50e15
0.12
0.10
0.08
0.08
0.06
IR13t 4.52e15
IR14t 5.62e15
0.06
0.04
0.04
0.02
0.02
0.00
0.00
0
2
4
6
Time
(msec)
ms
8
10
{k(297) = 2.1E-12 ;
k(221) = 1.0E-12)}
0
10
20
30
Time
ms (msec)
Interpretation: 1) Complexation occurs at lower T
2) Equilibrium reached quickly followed by HO2 rxns
Fitting Rise and Fall of Short time decay not possible
Method Developed:
• Fit Longer time decay with simple HO2 self-reaction
• Determine [HO2] at time = 0, w/out & w/ [Acetone]
0.16
• Correct for Cl + Acetone reaction
0.14
• Determine Keq from equilibrium concentrations 0.12
0.10
• Repeat for several [Acetone] at several T
0.08
•
 Keq(T)  ΔrH & ΔrS
0.06
IR05t [Ace] = 0
IR06t 2.24e15
IR09t 2.98e15
IR10t 3.50e15
IR13t 4.52e15
IR14t 5.62e15
0.04
0.02
0.00
0
2
4
6
ms
First must determine Cl + Acetone reaction at T=298K
8
10
Cl + CH3C(O)CH3 → HCl + CH3C(O)CH2
T =297 K
0.12
IR02t
IR03t
IR04t
IR05t
IR06t
IR07t
IR08t
IR09t
IR10t
IR11t
0.10
0.08
0.06
0.04
[Ace] = 0.0e15
2.18
4.06
5.48
5.41
7.09
9.93
12.8
17.5
20.5
O2 + CH3C(O)CH2 → CH3C(O)CH2OO (fast excess O2)
HO2 + CH3C(O)CH2OO → Products (k12f)
HO2 + HO2 → H2O2 + O2
0.02
10
20
ms
(k1f)
Fit with literature k12f and k1f from [Acetone] = 0 fit
0.00
0
(~10 sec)
30
Agree w/ lit. (no HO2 + Acetone reaction at Room T)
-3
2
1
0
-1
x10
x10
-3
3
2
1
0
-1
-2
-3
3
2
1
0
-1
-2
x10
x10
-3
Fits of Cl chemistry with Acetone & O2
2
1
0
-1
-2
0.10
0.10
0.04
60
40
0.02
20
0.00
0.00
0
6
8
0
10
2
4
6
8
10
x10
0
-1
2
4
6
8
0
3
2
1
0
-1
-2
8
10
6
8
10
2
0
60
40
20
-3
-3
60
IR signal/ (V x10 )
IR signal/ (V x10 )
-3
IR signal/ (V x10 )
-3
IR signal/ (V x10 )
6
70
60
20
4
-2
80
40
2
ms
80
60
20
10
-3
2
1
0
-1
-2
-3
-3
1
40
ms
x10
2
60
0
0
ms
x10
4
ms
-3
-3
-3
0.06
0.02
2
IR signal/ (V x10 )
0.04
IR signal/ (V x10 )
IR signal/ (V )
IR signal/ (V )
0.06
0
x10
80
80
0.08
0.08
40
20
50
40
30
20
10
0
0
0
0
2
4
6
ms
8
10
0
2
4
6
ms
8
10
0
0
2
4
6
ms
8
10
0
2
4
ms
0.16
0.14
Family of NIR HO2
decay curves at T = 221K
at varying acetone concentrations
0.12
IR05t
IR06t
IR09t
IR10t
IR13t
IR14t
0.10
0.08
0.06
[Ace] = 0
2.24e15
2.98e15
3.50e15
4.52e15
5.62e15
0.04
0.02
Cannot Fit Curves with Cl reactions
0.00
0
2
4
6
8
10
x10
-3
2
1
0
-1
-3
4
3
2
1
0
-1
-2
x10
x10
-3
ms
80
0.14
0.10
0.08
0.06
0.04
-3
-3
IR signal/ (V x10 )
IR signal/ (V x10 )
80
0.12
IR signal/ (V )
1.0
0.5
0.0
-0.5
-1.0
60
40
20
60
40
20
0.02
0.00
0
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0.0
0.5
1.0
2.5
3.0
3.5
0.0
-3
1.0
x10
-3
3
2
1
0
-1
-2
0.16
0.0
0.5
1.0
1.5
ms
2.0
2.5
3.0
1.0
0.0
-1.0
-1.0
0.10
0.08
0.06
0.04
60
-3
-3
IR signal/ (V x10 )
0.12
IR signal/ (V x10 )
80
0.14
IR signal/ (V )
2.0
ms
x10
x10
-3
ms
1.5
60
40
20
40
20
0.02
0
0
0.00
0.0
0.5
1.0
1.5
2.0
ms
2.5
3.0
0.0
0.5
1.0
1.5
2.0
ms
2.5
3.0
3.5
0.0
0.5
1.0
1.5
2.0
2.5
ms
Preliminary objective: Determine thermodynamics
3.0
3.5
x10
-3
Initial analysis: find [HO2]o([Ace]) at t = 0 s
to determine equilibrium concentration prior to
subsequent kinetics
1) [HO2]o(0) determined from fit &
corrected for Cl rxn with Acetone
1.0
0.0
2) [HO2]eq = [HO2]o([Ace]) determined from fit
60
-3
IR signal/ (V x10 )
-1.0
3) [Complex] = [HO2]o(0) – [HO2]o([Ace])
40
[Complex]
20
Keq
0
0.0
0.5
1.0
1.5
2.0
ms
2.5
3.0
3.5
=
[Ace] [HO2]o([Ace])
(excess)
Measure Keq at several atmospherically relevant temperatures
Kc(T) (cm3 molec-1)
T(K) (±2)
Kc(cm3/molec)
s (pph)
215.6
2.957E-16
12.7
220.7
1.506E-16
6.9
Van’t Hoff Plot: Rln(Kp) vs. 1/T
slope = -ΔrH°; intercept = ΔrS°
0.080
Van't Hoff Plot (not weighted)
0.075
222.5
1.227E-16
9.9
226.8
9.087E-17
13.7
227.6
7.856E-17
17.3
231.9
7.177E-17
22.5
232.3
5.977E-17
9.5
0.055
237.1
3.955E-17
5.8
0.050
242.7
2.589E-17
12.6
0.045
243.5
2.451E-17
17.4
0.040
245.9
2.961E-17
1.6
249.6
2.898E-17
5.2
254.5
1.335E-17
16.9
266.2
1.408E-17
23.7
272.3
7.671E-18
18.3
RlnK p
0.070
0.065
y = 30.97x - 0.0700
R2 = 0.9614
0.060
0.00360
0.00380
0.00400
0.00420
0.00440
-1
1/T(K )
ΔrH° = -31  1.7 kJ/mol
ΔrS° = -70  7.2 J/mol/K
ΔrG° = ΔrH° - T ΔrS°
Keq(T) = exp (- ΔrG° /RT)
0.00460
Comparison of Equilibrium Constants
Kc, cm3 molec-1
T (K)
200
Hermans et al. Cours et al. This Work
(from Keq equation)
2005
2007
3.05E-12
220
1.86E-16
7.40E-16
1.17E-17
1.50E-16
230
2.82E-14
7.50E-17
241
6.38E-15
3.75E-17
251
2.07E-15
273
298
2.06E-16
2.27E-17
4.28E-19
2.11E-17
8.64E-21
6.94E-18
2.41E-18
(extrapolated)
(extrapolated)
More Comparisons
Reaction Thermodynamics Compared to Calculated Values
Source
This Work
(T range = 215 – 272 K)
Hermans et al. (2005)
(van’t Hoff treatment)
Cours et al. (2007)
(van’t Hoff treatment: 200 – 298 K)
Aloisio et al. (2000)
(T = 200 K)
Aloisio et al. (2000)
(T = 300 K)
o
ΔrH
o
(kJ/mol)
ΔrS (J/mol/K)
-31
-70
-61.6
-153.3
-52.5
-188.9
-44.0
-95.5
-34.8
-109.3
Like complex!!!
Aloisio product:
Reaction to Complex
MOLECULAR
COMPLEX
HO2 + (CH3)2CO ⇄ (CH3)2CO---HO2
Herman et al.
↓
(CH3)2CO---H †
O▬O
Both Planar
o
C
a
l
c
u
l
a
t
i
o
n
s
Source
ΔrH
This Work
-31
(T range = 215 – 272 K)
(kJ/mol)
Hermans et al. (2005)
-44
Cours et al. (2007)
-36
Aloisio et al. (2000)
-44.0
(T = 200 K)
Aloisio et al. (2000)
(T = 300 K)
Aloisio et al.
Cours et al.
-34.8
Perpendicular
Comparison with Methanol and Water
Source
ΔrHo (kJ/mol)
HO2 + Acetone
-31
(This Work)
HO2 + Methanol
(Christiensen et al., 2006)
H2O + H2O
(Curtiss et al., 1979)
HO2Acetone
(Aloisio et al., 2000)
HO2Methanol
(Christiensen et al., 2006)
H2OH2O
(Klopper et al., 1995)
Do (kJ/mol)
-36.8
-15.0
37.3
35.7
21.0
Atmospheric Implications
(Just a taste.)
Analysis by
Hermans et al.:
Acetone removal (keff) from UT  Keq
At 190 K, keff = 5 x 10-6 s-1 which is
greater than acetone photolysis (4 x 10-7 s-1)
However, if our results are correct
and 2-HIPP is product:
Keq = 1.9 x 10-15
compared to Hermans et al.
Keq = 2.0 x 10-11
keff = 4.3 x 10-10 s-1
Summary
• Discovered reaction between HO2 + Acetone
• Developed Method to Determine Keq
for HO2/Carbonyl Reactions
• Able to Measure Keq Over Wide Temperature Range
Including Atmospherically Relevant Temperatures
• Thermodynamic Parameters Determined: Possible
Clues to Reaction Product and Its Structure
• Will Be Able to Determine Its Impact on the
Atmosphere
Future Work
1) Search for products (acetonylperoxy, 2-HIPP, Molecular Complex)
We have done some of this: T = 297 K acetonylperoxy: CH3C(O)CH2OO
σ(cm2/molec) at λuv = 280 nm
2.00E-20
H2O2
10
8
8
6
6
-3
HO2
4
2
4
2
0
0
-2
-2
-4
-4
0
5
10
15
[Ace] = 2.05E16
12
x10
acetonylperoxy
-3
0
10
x10
2.07E-18
[Ace] = 0
12
20
25
0
5
ms
10
15
20
25
ms
For (CH3)2C(OH)OO and (CH3)2C(O)OOH
No spectrum observed in uv; Calculations underway to estimate OH stretching
frequency and A-X transition
2) Measure forward rate constant
Very difficult work; has been accomplished for HO2 + methanol
3) Apply this method to many HO2 / Carbonyl systems:
MEK, Acetaldehyde, Formaldehyde
Acknowledgements
Mitchio
Okumura
Stan
Sander
Harry
Kroto
Aaron
Noell
The Future
Pomona
Chem Majors
Kira
Watson
Casey DavisVan Atta
Aileen
Hui
1st yr.
Caltech
Grad
Student
(not shown)
The research described in this paper was carried out at the Jet Propulsion Laboratory, California
Institute of Technology under contract to the National Aeronautics and Space Administration
*This research was supported by an appointment of Fred Grieman to the NASA Postdoctoral
Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated Universities
through a contract with NASA.