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

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.

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

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: +↔−

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

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

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;

|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>

|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>

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

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

|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 F1 F2

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

SEP Results of CH3O σ ~50MHz

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)

Correction of CH3O Assignment p +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

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

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)

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.

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