1. The A ← X ABSORPTION SPECTRUM OF 2-NITROOXYBUTYL PEROXY RADICAL
Nathan C. Eddingsaas, Kana Takematsu, Mitchio Okumura
64th OSU International Symposium on Molecular Spectroscopy

2. NO3•: The Primary Nighttime Atmospheric Oxidant
Concentrations:
Night time [NO3]: 100s of ppb
Daytime [OH]: < 1 ppt
NO3 + R=R
R(NO3)-R O2
R(NO3)-ROO
NO2
HO2
R(NO3)-ROOH NO
RO2
R(NO3)-ROH, R(NO3)-RHO, etc.
R(NO3)-ROONO2
k (298) with cis-2-butene
OH : 5.6 x10-12
NO3•: 3.5 x 10-13
O3: 1.2 x 10-16
Alkene k (298) cm3 molec-1 s-1 Ethene x Propene x cis/trans-2-butene /3.90 x α-pinene x 10-12
Atkinson, R.; Arey J. J. Chem. Rev. 2003, 103, 4605.

3. A←X Absorption Spectra of sec-Butyl Peroxy Radical
45 cm-1 conformer splitting
Origin of conformer A
Origin of conformer B
C-O-O bend of A
O-O stretch of A
ppm
cm-1
Weak cross section ~ cm2.
Bound-bound transition with well defined structure.
Can distinguish between different isomers and conformers.
Glover, B.; Miller, T. J. Phys. Chem. A 2005, 109, 1191.

4. Effect of Electron Withdrawing Group on A←X Transition
0-0: cm-1
0-0: 7383 cm-1
Pushkarsky, et. al. J. Chem. Phys. 2000, 112,
Zalubovksy, et. al. Chem. Phys. Lett. 2001, 335, 298.
- 727 cm-1
CH3O2
CF3O2
(red shift)
Addition of NO3 to peroxy radical should red shift the absorption bands.

5. CRDS Experimental Setup
10 % cis/trans-2-butene in N2 P: 3-5 Torr
NO3 from N2O5 ~1.5 torr oxygen carrier gas ~150 torr
Pump
Press. readout
heating tape (42°C)
Ringdown mirror (99.99% reflective)
thermocouple
Total pressure in cell ~ 170 torr
Residence time ~ 4 sec.

6. Initial Reactions Within Cell
At 42 °C and 170 torr, nitrooxybutyl peroxy radical should dominate.

7. CRDS of Reactents: 2-butene and NO3•
300
200
Absorbance (ppm)
100
7000
7100
7200
7300
7400
7500
7600
Wavenumbers (cm-1)
For more information on NO3• see Kana’s talks: WJ11 and RD02.

8. Reaction of 2-butene, NO3•, and O2
600
7120 cm-1
Reaction products
2-butene
500
400
7166 cm-1
Absorbance (ppm)
300
Origin of sec-butyl peroxy radical (7560 cm-1)
200
100
7000
7100
7200
7300
7400
7500
7600
Wavenumbers (cm-1)
New peaks observed.

9. Identification of New Peaks
Tentatively assigned to the origin of A←X transition of 2-nitrooxybutyl peroxy radical.
Peaks 440 cm-1 redshifted from unsubstituted peroxy.
46 cm-1 separation (45 cm-1 observed from sec-butyl peroxy radical).
Shows some pressure dependency.
7100
7200
200
300
400
500
600
Absorbance (ppm)
Wavenumbers (cm-1)
7150
7050
7250
7120 cm-1
7166 cm-1

10. Computation of Nitrooxyethyl Peroxy
B3LYP/6-31+G(d,p) *
transition freq of A← X transition ~ cm-1
( cm-1 from ethylperoxy)
* Shown by the Miller group to model peroxy radicals very well.

11. Computation of Nitrooxyethyl Peroxy
Forced into Cs symmetry
Transition freq~ cm-1
cm-1 from ethylperoxy.
cm-1 from C1 transition (-230cm-1 for ethyl peroxy radical).
Modeled electronegative CF3O2• with similar difficulties.

12. CRDS of Region of O-O Stretch
CRDS of reaction of 2-butene with NO3• and O2
125
NO3•
100 75
Absorbance (ppm) 50 25
8000
8050
8100
8150
8200
8250
Wavenumbers (cm-1)
Peroxy radical O-O stretch typically observed ~ 1000 cm-1 from origin.

13. Normalized Intensity (au) No unidentified structure observed.
New Feature From HNO3
1.0
Sum
NO3+Butene
NO3
2-Butene
HNO3
Normalized Intensity (au)
0.5
8000
8050
8100
8150
8200
8250
Wavenumbers (cm-1)
No unidentified structure observed.

14. Normalized Intensity (au)
Effect of Temperature
8000
8050
8100
8150
8200
8250
0.5
1.0
Normalized Intensity (au)
Wavenumbers (cm-1)
NO3+ Butene 115 °C
NO3
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.

15. 2-nitrooxybutyl peroxy radical
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 radical show red shift of substituted peroxy.
Possible observation of O-O stretch of nitrooxybutyl peroxy radical.
7100
7200
200
400
600
Absorbance (ppm)
Wavenumbers (cm-1)
7150
7050
7250
2-nitrooxybutyl peroxy radical

16. Follow up and Future Work
Use higher flow rate to minimize secondary chemistry.
Confirm assignment of nitrooxybutyl peroxy radical by chemical means. Addition of NO Using deuterated butene.
Obtain better computational simulations of model compound and exact compound.
Extend system to other alkenes and dienes.
Pulsed photolysis source to study kinetics.
Look at products from reactions of alkenes with other oxidants such as OH• and O3.

17. Acknowledgments Prof. Mitchio Okumura Kana Takematsu Sigrid Barklund
Funding:
Camille & Henry Dreyfus Postdoctoral Program in Environmental Chemistry
EPA STAR Graduate Fellowship (Kana)
NASA UARP