1. Jinjun Liu, Ming-Wei Chen, John T. Yi,
High-Resolution Stimulated Emission Pumping (SEP) Spectroscopy Applied to The Methoxy Radical
Jinjun Liu, Ming-Wei Chen, John T. Yi,
and Terry A. Miller
Laser Spectroscopy Facility
Department of Chemistry
The Ohio State University
6/21/2007

2. Outline Talk I (RF01): Talk II (RF02): Motivation and goals
SEP experiment
Experimental apparatus and calibration method
Model compound for SEP experiment of isotopomers
SEP spectroscopy of CH3O
Global fitting
Spectra analysis of microwave, LIF, and SEP results
Summary and acknowledgement
Talk II (RF02):
Asymmetrically deuterated isotopomers.

3. Motivation
Alkoxy radicals (RO·) are key components in the oxidation of hydrocarbons both in combustion and in the atmosphere.
Methoxy (CH3O), the smallest alkoxy radical is an interesting molecule for dynamic studies and has also very important theoretical interest due to its Jahn-Teller effect, coupled to spin-orbit interaction.
The partial deuteration of the methoxy radical (RF02).
Breaks the molecular symmetry.
Turns Jahn-Teller effect to pseudo-Jahn-Teller effect.
Benchmark for ab initio calculations

4. Spectroscopy of Methoxy Radicals
1Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984)
2T. Momose, Y. Endo, E. Hirota, and T. Shida, J. Chem. Phys. 88, 5338 (1988)
3D. E. Powers, M. B. Pushkarsky, and T. A. Miller, J. Chem. Phys. 106, 6863 (1997)
5J. Liu, J. T. Yi, V. Starkursky, and T. A. Miller, 61st International Symposium on Molecular Spectroscopy, TJ04&05 (2006).
4A. Geers, J. Kappert, F. Temps, and J. W. Wiebrecht, J. Chem. Phys. 101, 3618 (1994)
resolution~1.2GHz
resolution~250MHz
Microwave1,2
SEP4
LIF3
LIF5
SEP
~60 cm-1
resolution~3GHz
Δ∑=0
ΔK=0
parity: +↔−

5. Experimental Apparatus: Overview
DG535 Pulse Generator
General Valve Controller
Photolysis
XeF Excimer Laser T0
Q-Switch
Dump
Nd:YAG Laser
Sirah Dye Laser
SHG
Flash Lamp
program
T0 / GPIB
PC #2
CH3ONO
/ 1st run Ne
synchronizing
PMT
Nozzle
PC #1
Lens
Frequency reading
Ar+ Laser
Ring Laser
Pulsed Dye Amplifier
SHG
XeCl Excimer Laser
Pump

6. Experimental Apparatus: Ring Laser & Calibration System
Etalon
Chopper
(2KHz)
λ/2 Plate
PBS PD
Calibration
System I2
50cm
~100mW
1-3 mW
LIF resolution (FWHM): ~250MHz
LIF accuracy (1σ): ~50MHz
to dye amplifier
CW Ring
Dye Laser
Ar+ Laser
Lock-in
Computer

7. Notations of Hund’s case (a) and (b)
J - total angular momentum of the molecule;
P - projection of J onto the molecule-fixed z or a axis;
Σ=±1/2 - projection of S (electron spin) onto the z or a axis;
p =±1 - parity.
: Hund’s case (b)
N - rotational angular momentum;
K - projection of N onto the molecule-fixed z or a axis;

8. |J',N', K', p'> ←
|J",P",Σ", p">
|1/2,1,0,-1>
|3/2,3/2,1/2,1>
|3/2,1,0,-1>
|J',N',K', p'> ←
|J",P",Σ", p">
|1/2,0,0,1>
|3/2,3/2,1/2,-1>

9. |J',N', K',p'> |1/2,0,0,1> |J",P",Σ",p"> |3/2,1/2,-1/2,±1>+1 -1
Pump
Dump
|J",P",Σ",p">
|3/2,1/2,-1/2,±1>
|1/2,1/2,-1/2,±1>
|5/2,3/2,1/2,±1>
|3/2,3/2,1/2,±1>

10. |J',N',K',p'> →
|J'',P'',Σ'',p''>
|1/2,0,0,1>
|1/2,1/2,-1/2,-1>

11. *LIF excited by dump laser
SEP Spectrum of CH3O
*LIF excited by dump laser

12. |J',N',K',p'> ← |J'',P'',Σ'',p''> F1: |1/2,1,0,-1>
|3/2,3/2,1/2,1>
F2:
|3/2,1,0,-1>
0.12cm-1
F F2

13. SEP Spectrum of CH3O J’=1/2 J’=3/2
High-resolution pump F1, moderate-resolution dump
J’=3/2
High-resolution pump F2, moderate-resolution dump
Moderate-resolution pump F1+F2, high-resolution dump

14. SEP Results of CH3O
σ ~50MHz

15. Effective Hamiltonian:
ground state (2E):a HEFF = HROT + HCOR + HSO + HSR + HJT + HCD
excited state (2A1):b,c,d HEFF = HROT + HCOR + HSR + HCD
Spin-orbit interaction
Spin-rotation interaction
Rotational Hamiltonian
Coriolis interaction
Jahn-Teller interaction
Centrifugal distortion
aY. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984)
bX. Liu, C. P. Damo, T.-Y. Lin, S. C. Foster, P. Misra, L. Yu, and T. A. Miller, J. Phys. Chem. 92, 5914 (1988)
cX. Liu, S. C. Foster, J. M. Williamson, L. Yu, and T. A. Miller, Mol. Phys. 69, 357 (1990)
dD. E. Powers, M. B. Pushkarsky, and T. A. Miller, J. Chem. Phys. 106, 6863 (1997)

16. Correction of CH3O Assignmentp +1 -1
Pump (LIF)
Dump (SEP)
|J',N',K',p'>
|3/2,1,0,-1>
|3/2,3/2,1/2,±1>
|J",P",Σ",p">
|5/2,1/2,-1/2,±1>
|3/2,1/2,-1/2,±1>
|1/2,1/2,-1/2,±1>
|5/2,3/2,1/2,±1>
Modified aζed and parity assignment in this work
prediction1,2 − observation ~ − 20GHz
prediction1,2 − observation ~ 2GHz
1Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984)
2T. Momose, Y. Endo, E. Hirota, and T. Shida, J. Chem. Phys. 88, 5338 (1988)
|J",P",Σ",p">
|3/2,3/2,1/2,±1>
|5/2,1/2,-1/2,±1>
|3/2,1/2,-1/2,±1>
|1/2,1/2,-1/2,±1>
|5/2,3/2,1/2,±1>
aζed = −61.43(9) cm-1
aζed = −62.24(17) −61.43(9) cm-1

17. Global summary of data
aY. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984)
bThis work.

18. Ground State Parameters
Rotational
Centrifugal Distortion
Coriolis
Spin-Orbit
Spin-Rotation
Jahn-Teller
aT. Momose, Y. Endo, E. Hirota, and T. Shida, J. Chem. Phys. 88, 5338 (1988)
bThis work
cFixed to ε2a*(B/A)
d2.5σ in parentheses
eY. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984)

19. Summary
New SEP apparatus with both high-resolution (FWHM~250MHz) and high-accuracy (σ~50MHz).
High-resolution SEP spectra of CH3O.
Direct measurement of E1/2 component of the electronic ground state.
New assignment and molecular constants from the global fitting involving microwave, LIF, and SEP
Spin-orbit splitting ( )
Parity assignment and Jahn-Teller related parameters (ε1, h1, h2…)
Model compound of experimental setup and theory for isotopomers.

20. Acknowledgement Funding: NSF Your attention!
Miller’s group:
Dr. Miller
Patrick Dupré
Shenghai Wu (previous member)
Patrick Rupper
John T. Yi (previous member)
Jinjun Liu (previous member)
Dmitry Melnik
Erin Sharp
Gabriel Just
Funding: NSF
Your attention!
Next Talk: RF02, Jinjun Liu