Department of Chemistry California Institute of Technology Importance of NO 3 to oxidation of...
17
Department of Chemistry California Institute of Technology Importance of NO 3 • to oxidation of alkenes in the atmosphere. Cavity Ringdown Spectroscopy of reaction of 2-butene with NO 3 Computational studies of nitrooxyethyl peroxy radical. The A ← X ABSORPTION SPECTRUM OF 2-NITROOXYBUTYL PEROXY RADICAL Nathan C. Eddingsaas , Kana Takematsu, Mitchio Okumura 64 th OSU International Symposium on Molecular Spectroscopy
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Transcript of Department of Chemistry California Institute of Technology Importance of NO 3 to oxidation of...
Department of ChemistryCalifornia Institute of Technology
• Importance of NO3• to oxidation of alkenes in the atmosphere.
• Cavity Ringdown Spectroscopy of reaction of 2-butene with NO3•.
• Computational studies of nitrooxyethyl peroxy radical.
The A ← X ABSORPTION SPECTRUM OF 2-NITROOXYBUTYL PEROXY RADICAL
Nathan C. Eddingsaas, Kana Takematsu, Mitchio Okumura
64th OSU International Symposium on Molecular Spectroscopy
NO3•: The Primary NighttimeAtmospheric Oxidant
Alkene k (298) cm3 molec-1 s-1 Ethene 2.05 x 10-16 Propene 9.49 x 10-15 cis/trans-2-butene 3.52/3.90 x 10-13 α-pinene 6.16 x 10-12
Atkinson, R.; Arey J. J. Chem. Rev. 2003, 103, 4605.
NO3 + R=R
R(NO3)-R
O2
R(NO3)-ROONO2HO2
R(NO3)-ROOHNORO2
R(NO3)-ROH, R(NO3)-RHO, etc.
R(NO3)-ROONO2
Concentrations:Night time [NO3]: 100s of ppb
Daytime [OH]: < 1 ppt
k (298) with cis-2-buteneOH : 5.6 x10-12
NO3•: 3.5 x 10-13
O3: 1.2 x 10-16
Glover, B.; Miller, T. J. Phys. Chem. A 2005, 109, 1191.
pp
m
cm-1
C-O-O bendof A
O-O stretchof A
Origin of conformer A
Origin of conformer B
45 cm-1 conformer splitting
A←X Absorption Spectra of sec-Butyl Peroxy Radical
Weak cross section ~ 10-20 cm2.Bound-bound transition with well defined structure.Can distinguish between different isomers and conformers.
Effect of Electron Withdrawing Group
on A←X Transition
CH3O2 CF3O2 - 727 cm-1
(red shift)
0-0: 6656 cm-10-0: 7383 cm-1
Pushkarsky, et. al. J. Chem. Phys. 2000, 112, Zalubovksy, et. al. Chem. Phys. Lett. 2001, 335, 298.
Addition of NO3 to peroxy radical should red shift the absorption bands.
CRDS Experimental Setup
Pump
thermocouple
Press. readout
heating tape (42°C)
10 % cis/trans-2-butenein N2 P: 3-5 Torr
NO3 from N2O5 ~1.5 torroxygen carrier gas ~150 torr
Ringdown mirror(99.99% reflective)
Total pressure in cell ~ 170 torrResidence time ~ 4 sec.
Initial Reactions Within Cell
At 42 °C and 170 torr, nitrooxybutyl peroxy radical should dominate.
N2O5NO3 + NO2
+ NO3
ONO2
O
+ NO2
ONO2
OO
O2 , M
NO2
ONO2
OONO2
CRDS of Reactents: 2-butene and NO3•
7000 7100 7200 7300 7400 7500 76000
100
200
300
Ab
so
rban
ce
(pp
m)
Wavenumbers (cm-1)
2-butene
NO3•
For more information on NO3• see Kana’s talks: WJ11 and RD02.
Reaction of 2-butene, NO3•, and O2
7000 7100 7200 7300 7400 7500 76000
100
200
300
400
500
600
Ab
so
rban
ce
(pp
m)
Wavenumbers (cm-1)
7120 cm-1
7166 cm-1
New peaks observed.
Origin of sec-butyl peroxy radical (7560 cm-1)
Reaction products
2-butene
Identification of New Peaks
Peaks 440 cm-1 redshiftedfrom unsubstituted peroxy.
46 cm-1 separation(45 cm-1 observed fromsec-butyl peroxy radical).
Shows some pressuredependency.
Tentatively assigned to the origin of A←X transition of 2-nitrooxybutyl peroxy radical.
7100 7200
200
300
400
500
600
Ab
sorb
ance
(p
pm
)
Wavenumbers (cm-1)71507050 7250
7120 cm-1
7166 cm-1
ONO2
OO
Computation of Nitrooxyethyl Peroxy
transition freq of A← X transition ~ 7458.264 cm-1
(-133.736 cm-1 from ethylperoxy)
B3LYP/6-31+G(d,p) *
* Shown by the Miller group to model peroxy radicals very well.
Computation of Nitrooxyethyl Peroxy
Transition freq~ 7285.666 cm-1
-76.33429 cm-1 from ethylperoxy.
-172.598 cm-1 from C1 transition (-230cm-1 for ethyl peroxy radical).
Forced into Cs symmetry
Modeled electronegative CF3O2• with similar difficulties.
CRDS of Region of O-O Stretch
8000 8050 8100 8150 8200 82500
25
50
75
100
125A
bs
orb
anc
e (p
pm
)
Wavenumbers (cm-1)
NO3•
CRDS of reaction of 2-butene with NO3• and O2
Peroxy radical O-O stretch typically observed ~ 1000 cm-1 from origin.
New Feature From HNO3
8000 8050 8100 8150 8200 82500
0.5
1.0N
orm
aliz
ed In
ten
sit
y (
au
)
Wavenumbers (cm-1)
NO3+ButeneNO3 2-Butene HNO3 Sum
No unidentified structure observed.
Effect of Temperature
8000 8050 8100 8150 8200 82500
0.5
1.0N
orm
aliz
ed In
ten
sit
y (
au
)
Wavenumbers (cm-1)
NO3+ Butene 115 °CNO3 2-Butene HNO3 Sum
*
New peak ~1100 cm-1 from 7120 cm-1 peak.Typically O-O stretch in peroxy radical is ~1000 cm-1 from origin.
Summary
CRDS of reaction of 2-butene with NO3• has been observed.
Peaks at 7120 cm-1 and 7166 cm-1 have been tentatively assigned to A-X origin of nitrooxybutyl peroxy radical.
Preliminary computation of nitrooxyethyl peroxy radicalshow red shift of substituted peroxy.
Possible observation of O-O stretch of nitrooxybutyl peroxy radical.
7100 7200
200
400
600
Ab
sorb
ance
(p
pm
)
Wavenumbers (cm-1)71507050 7250
ONO2
OO
2-nitrooxybutyl peroxy radical
Follow up and Future Work
Use higher flow rate to minimize secondary chemistry.
Confirm assignment of nitrooxybutyl peroxy radical by chemical means.
Addition of NOUsing deuterated butene.
Obtain better computational simulations of model compoundand exact compound.
Extend system to other alkenes and dienes.
Pulsed photolysis source to study kinetics.
Look at products from reactions of alkenes with otheroxidants such as OH• and O3.
Acknowledgments
Prof. Mitchio Okumura
Kana Takematsu
Sigrid Barklund
Funding:
Camille & Henry Dreyfus PostdoctoralProgram in Environmental Chemistry
EPA STAR Graduate Fellowship (Kana)
NASA UARP
