1. International Symposium on Molecular Spectroscopy, 2017
Direct measurement of OD+CO branching kinetics using time-resolved frequency comb spectroscopy
Bryce J Bjork
JILA and University of Colorado at Boulder
International Symposium on Molecular Spectroscopy, 2017

2. A key reaction in atmospheric and combustion chemistry
The OH+CO Reaction
A key reaction in atmospheric and combustion chemistry
Strong pressure and anomalous temperature dependencies
OH+CO
OH…CO
TS1
trans-HOCO
cis-HOCO
TS2
TS3
H-CO2
TS5
H+CO2
-120
-80
-40 40
Energy (kJ/mol)
TS4
Reaction Progress
kT = 2.5 kJ/mol at 300 K
Bjork, Science (2016) and Nguyen et al. Phys. Chem Lett, 3, 1549 (2012)

3. A key reaction in atmospheric and combustion chemistry
The OH+CO Reaction
A key reaction in atmospheric and combustion chemistry
Strong pressure and anomalous temperature dependencies
OH+CO
OH…CO
TS1
trans-HOCO
cis-HOCO
TS2
TS3
H-CO2
TS5
H+CO2
-120
-80
-40 40
Energy (kJ/mol)
TS4
Reaction Progress
kT = 2.5 kJ/mol at 300 K
Bjork, Science (2016) and Nguyen et al. Phys. Chem Lett, 3, 1549 (2012)

4. Imagine you had a tool to see all of these species in real time…
The OH+CO Reaction
Imagine you had a tool to see all of these species in real time…
OH+CO
OH…CO
TS1
trans-HOCO
cis-HOCO
TS2
TS3
H-CO2
TS5
H+CO2
-120
-80
-40 40
Energy (kJ/mol)
TS4
Reaction Progress
kT = 2.5 kJ/mol at 300 K

5. The Optical Frequency Comb
Laser Pulse
Time
Frequency

6. The Optical Frequency Comb
Laser Pulse
Time
Frequency

7. (1) (2) Our tool Mid-IR Frequency Comb Source (3-5 mm) Mid-IR Camera
Time (log scale)
Wavenumber
grating
(1)
(2)
VIPA etalon

8. (1) (2) (2) Our tool Mid-IR Frequency Comb Source (3-5 mm)
Optical Enhancement Cavity
Mid-IR Camera
Time (log scale)
Wavenumber
grating
(1)
(2)
(2)
VIPA etalon

9. (1) (2) (3) (2) Our tool Mid-IR Frequency Comb Source (3-5 mm)
Optical Enhancement Cavity
Spatially Dispersive VIPA Spectrometer
(3)
Mid-IR Camera
Time (log scale)
Wavenumber
grating
(1)
(2)
(2)
VIPA etalon

10. + + + Reaction Scheme (( )) 266 nm O(1D) O2 O3 D OD O(1D) D2 OD CO D
(( )) D
CO2
[M]
T = 300 K, Ptotal ≈ 100 Torr

11. trans-DOCO TS3 40 TS2 TS1 OH+CO OH…CO Energy (kJ/mol) TS5 -40 H-CO2
trans-HOCO
cis-HOCO
TS2
TS3
H-CO2
TS5
H+CO2
-120
-80
-40 40
Energy (kJ/mol)
TS4
Reaction Progress
kT = 2.5 kJ/mol at 300 K

12. trans-DOCO P Q R
Data
trans-DOCO OD

13. trans-DOCO

14. cis-DOCO TS3 40 TS2 TS1 OH+CO OH…CO Energy (kJ/mol) TS5 -40 H-CO2 TS4
trans-HOCO
cis-HOCO
TS2
TS3
H-CO2
TS5
H+CO2
-120
-80
-40 40
Energy (kJ/mol)
TS4
Reaction Progress
kT = 2.5 kJ/mol at 300 K

15. cis-DOCO

16. D+CO2 TS3 40 TS2 TS1 OH+CO OH…CO Energy (kJ/mol) TS5 -40 H-CO2 TS4 -80
trans-HOCO
cis-HOCO
TS2
TS3
H-CO2
TS5
H+CO2
-120
-80
-40 40
Energy (kJ/mol)
TS4
Reaction Progress
kT = 2.5 kJ/mol at 300 K

17. D+CO2

18. Reactants and Products
trans-DOCO
cis-DOCO
CO2

19. Concentrations vs. Time1b
OD + CO
DOCO*
D + CO2 M 1a
DOCO

20. D+CO2
OD + CO
DOCO*
D + CO2
DOCO M 1a 1b
CO2 Formation
OD Decay

21. Mass Balance Our measurement Golden et al. (1998)
OD + CO
DOCO*
D + CO2
DOCO M 1a 1b
Our measurement
Golden et al. (1998)
Paraskevopoulos & Irwin (1982)

22. Isomerization

23. Isomerization

24. Simple Isomerization A B
Initially, we start with [A]/[B] = 1

25. Isomerization (+5) (+2.5) (+0) (-2.5) (-5) [CO] formation
equilibrium / steady-state

26. Isomerization Rate formation isomerization loss cis → trans
trans → cis

27. Summary TS3 40 TS2 TS1 OH+CO OH…CO Energy (kJ/mol) TS5 -40 H-CO2 TS4
trans-HOCO
cis-HOCO
TS2
TS3
H-CO2
TS5
H+CO2
-120
-80
-40 40
Energy (kJ/mol)
TS4
Reaction Progress

28. Acknowledgements Mid-IR Team Thinh Bui Oliver Heckl Kana Iwakuni
Bryce Bjork
(now at Vienna)
Bryan
Changala
Collaborators:
Mitchio Okumura (Caltech)
Dave Patterson (Harvard)
John Doyle (Harvard)
Garrett Cole (CMS)
Ben Spaun
Jun Ye

29. Thank you for your attention!