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ROTATIONALLY RESOLVED A 2 A 1 - X 2 E ELECTRONIC SPECTRA OF SYMMETRIC METHOXY RADICALS: CH 3 O AND CD 3 O (RI08) Laser Spectroscopy Facility Department.

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Presentation on theme: "ROTATIONALLY RESOLVED A 2 A 1 - X 2 E ELECTRONIC SPECTRA OF SYMMETRIC METHOXY RADICALS: CH 3 O AND CD 3 O (RI08) Laser Spectroscopy Facility Department."— Presentation transcript:

1 ROTATIONALLY RESOLVED A 2 A 1 - X 2 E ELECTRONIC SPECTRA OF SYMMETRIC METHOXY RADICALS: CH 3 O AND CD 3 O (RI08) Laser Spectroscopy Facility Department of Chemistry The Ohio State University 6/19/2008 ~~

2 Subsequent talk:  Isotope dependence.  Asymmetrically deuterated isotopomers. Subsequent talk:  Isotope dependence.  Asymmetrically deuterated isotopomers. Present talk :  Motivations and aims.  Experiment.  Doable experimental apparatus for both Laser Induced Fluorescence (LIF) and Stimulated Emission Pumping (SEP).  Calibration method.  Spectroscopy of CH 3 O and CD 3 O.  Global fitting and spectral analysis.  Model compounds for other isotopomers.  Summary. Present talk :  Motivations and aims.  Experiment.  Doable experimental apparatus for both Laser Induced Fluorescence (LIF) and Stimulated Emission Pumping (SEP).  Calibration method.  Spectroscopy of CH 3 O and CD 3 O.  Global fitting and spectral analysis.  Model compounds for other isotopomers.  Summary.

3  Alkoxy radicals (RO·) are key components in the oxidation of hydrocarbons both in combustion and in the atmosphere.  Methoxy (CH 3 O·), the smallest alkoxy radical is an interesting molecule which has very significant theoretical interest due to the Jahn-Teller effect coupled to spin-orbit interaction, the former is also relevant to conical intersection for chemical reactions.  Benchmark for ab initio calculations and standard for isotopic analysis.

4 LIF 3 SEP Microwave 1,2 1 Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984) 2 T. Momose, Y. Endo, E. Hirota, and T. Shida, J. Chem. Phys. 88, 5338 (1988) 5 J. Liu, J. T. Yi, V. Starkursky, and T. A. Miller, 61 st International Symposium on Molecular Spectroscopy, TJ04&05 (2006). 3 D. E. Powers, M. B. Pushkarsky, and T. A. Miller, J. Chem. Phys. 106, 6863 (1997) resolution~250MHz resolution~3GHz 4 A. Geers, J. Kappert, F. Temps, and J. W. Wiebrecht, J. Chem. Phys. 101, 3618 (1994) ΔΣ=0 ΔP=0 SEP 4 ~60 cm -1 LIF 5 ΔP=±1 ΔΣ=±1 p +1 Reflection parity (p): Reflection partity (p):

5 | J',N', K', p'> |1/2,0,0,1> | J",P",Σ", p " > |3/2,3/2,1/2,±1> |3/2,1/2,-1/2,±1> |1/2,1/2,-1/2,±1> |5/2,3/2,1/2,±1> Pump Dump p +1 Hund’s case (a) Hund’s case (b)

6 CH 3 ONO (CD 3 ONO) / 1 st run Ne General Valve ControllerDG535 Pulse Generator XeF Excimer Laser XeCl Excimer Laser Ar + Laser Nd:YAG Laser Sirah Dye Laser Pulsed Dye Amplifier PC #1 PC #2 Nozzle Ring Laser T0T0 PMT SHG Frequency reading Photolysis Dump Pump Q-Switch Flash Lamp T 0 / GPIB T0T0 program synchronizing Lens

7 CH 3 OCD 3 O

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

9

10

11  ground state ( 2 E): a H EFF = H ROT + H COR + H SO + H SR + H JT + H CD Rotational Hamiltonian Coriolis interaction Spin-orbit interaction Spin-rotation interaction Jahn-Teller interaction Centrifugal distortion  excited state ( 2 A 1 ): b,c,d H EFF = H ROT + H COR + H SR + H CD a Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984) b X. Liu, C. P. Damo, T.-Y. Lin, S. C. Foster, P. Misra, L. Yu, and T. A. Miller, J. Phys. Chem. 92, 5914 (1988) c X. Liu, S. C. Foster, J. M. Williamson, L. Yu, and T. A. Miller, Mol. Phys. 69, 357 (1990) d D. E. Powers, M. B. Pushkarsky, and T. A. Miller, J. Chem. Phys. 106, 6863 (1997)

12 aζ e d 1,2 = −62.24(17)cm -1 1 Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984) 2 T. Momose, Y. Endo, E. Hirota, and T. Shida, J. Chem. Phys. 88, 5338 (1988) aζ e d = −61.4994(39) cm -1 |N',J',K',p'> |1,3/2,0,-1> |J",P",Σ",p"> |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> p +1 MW LIF SEP |N',J',K',p'> |1,3/2,0,-1> |J",P",Σ",p"> |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> |N',J',K',p'> |1,3/2,0,-1> |J",P",Σ",p"> |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>

13 a CH 3 O: Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984) ; CD 3 O: Y. Endo, private communication. b CH 3 O: T. Momose, Y. Endo, E. Hirota, and T. Shida, J. Chem. Phys. 88, 5338 (1988); CD 3 O: Y. Endo, private communication. c This work.

14 CH 3 O, 3 2 0 bandCD 3 O, 3 2 0 band

15 CH 3 OCD 3 O

16 Rotational Spin-Orbit Coriolis Centrifugal Distortion Spin-Rotation Jahn-Teller b This work c Fixed to ε 2a *(B/A) d 2.5σ in parentheses e T. Momose, Y. Endo, E. Hirota, and T. Shida, J. Chem. Phys. 88, 5338 (1988) a Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984) f fixed to CD 3 F value. g Y. Endo, private communication.

17  LIF and SEP spectra are taken with both high-resolution (FWHM~250MHz) and high-accuracy (σ~50MHz).  Direct measurement of E 1/2 component of the electronic ground state.  Spin-orbit splitting ( )  Correction to parity assignments and Jahn-Teller related parameters ( ε 1, h 1, h 2 …) from the global fitting involving microwave, LIF, and SEP  Available isotope (CH 3 O, CD 3 O) data for isotopic analysis. (RI09)  LIF and SEP spectra are taken with both high-resolution (FWHM~250MHz) and high-accuracy (σ~50MHz).  Direct measurement of E 1/2 component of the electronic ground state.  Spin-orbit splitting ( )  Correction to parity assignments and Jahn-Teller related parameters ( ε 1, h 1, h 2 …) from the global fitting involving microwave, LIF, and SEP  Available isotope (CH 3 O, CD 3 O) data for isotopic analysis. (RI09)

18 The METHOXY team: Dr. Miller Dmitry Melnik Jinjun Liu (alumni) Funding: NSF Your attention! NEXT: RI09, given by Dmitry Melnik Other Miller group members: Shenghai Wu (alumni) Patrick Rupper (alumni) John T. Yi (alumni) Jinjun Liu (alumni) Erin Sharp (alumni) Gabriel Just Phillip Thomas Linsen Pei Rabi Chhantyal-Pun

19 Isotopic Relations (2) Spin-RotationJahn-Teller

20 Isotopic Relations (1) Spin-Rotation Jahn-Teller

21 Decomposition of Parameters For an arbitrary parameter of the effective Hamiltonians First order correction to the vibronic energy (H ROT ) Second order perturbation theory from the matrix elements of H ROT +H SO Vibronic levels in DIFFERENT electronic states Vibronic levels in the SAME electronic states h 1, h 2 ε 1, ε 2a, ε 2b

22  I fl DUMP PUMP s1’s1’ I fl DUMP PUMP s1s1 s0s0  The simple normalization technique works fine except when “dump” laser excites cold band of target molecule. SEP=(S 1 -S 1 ’ ) / S 0 Stimulated Emission Pumping (SEP: Pump-Dump)

23 John-Teller active mode. Allowed due to 2 E symmetry of the X state and the Jahn-Teller distortion. ~ LIF Spectrum of CH 3 O * S.C.Foster, X.P.Misra, T.D.Lin, C.P.Damo, C.C.Carter, and T.A.Miller, J. Phys. Chem. 92, 5914 (1988)

24 a. Broader than the other three isotopomers (~250MHz). b. B. Bodermann, H. Knöckel, E. Tiemann, IodineSpec4, Toptica Photonics, Munich, Germany, (2002)

25 Lifting of Vibronic Degeneracy

26 Hamiltonian Elements, asym. terms  Lifting of vibronic degeneracy:  Rotational  Coriolis  Spin-orbit  Spin-rotation

27  Effective Hamiltonian: H EFF = H ROT + H COR + H SR + H CD  Basis sets: “Hund’s case a” used.  To utilize the global fitting  Can be converted to “Hund’s case b” through unitary transformation * Effective Hamiltonian: excited state ( 2 e/ 2 a) * I. Kalinovski, Ph.D. Dissertation (2001)

28 ν 6 ’ ( a’ ) ν 6 ” ( a” ) ν 3 ( a’ ) ν 3 ( a 1 ) Transition Types and Selection Rules CH 3 O(C 3v )CHD 2 O(C s ) M _|_ + only M _|_ only M _|_ + & M || M _|_ - & M || HD ν 6 ( e ) M _|_ & M ||  M _|_  P’=P”±1  M _|_ +  P’=P”-1  M _|_ -  P’=P”+1  M ||  P’=P”  M _|_  P’=P”±1  M _|_ +  P’=P”-1  M _|_ -  P’=P”+1  M ||  P’=P” Selection Rules of P(~K+ Σ) Selection Rules of P(~K+ Σ)

29 Vibronic Interaction for 2 e- 2 e transition a 1 (Q a ) CH 3 O (C 3v ) CHD 2 O (C s ) a’ (Q a, Q x ) a” (Q y ) e (Q x, Q y ) * G. Herzberg Molecular Spectra and Molecular Structure III  M _|_ + : dominant  M _|_ - : moderate  M ||  M _|_ -  M ||

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

31 |N',J',K', P '> |1,3/2,0,-1> |J",K",Σ", P "> |3/2,1,1/2,±1> |J,K,Σ, P > |5/2,1,-1/2,±1> |3/2,1,-1/2,±1> |1/2,1,-1/2,±1> |5/2,1,1/2,±1> Pump Dump P +1 |1,1/2,0,-1> Moderate-resolution pump

32 |N',J',K', P '> → |J,K,Σ, P > D1:|1,1/2,0,-1>→|1/2,1,-1/2,1> D2:|1,3/2,0,-1>→|1/2,1,-1/2,1> D1D2

33 n’=0  n”=0 + microwave selection rules (for microwave spectra) n’=1  n”=0 + 2 e- 2 e selection rules (for 6 1 0 band) or + a’/a”- 2 e selection rules (for 6’ 1 0 band) n’=2  n”=0 + 2 a- 2 e selection rules (for 3 2 0 band) Selection Rules Global Fitting n=2, 3 2 n=1, 6 1 n=0, 0 0 0 Energy Levels Global Hamiltonian H 2a + T e (3 2 0 ) H 2a + T e (3 2 0 ) H 2e + T e (6 1 0 ) H 2e + T e (6 1 0 ) H 2e n =2n =2 n =1n =1 n =0n =0 n =2n =2 n =1n =1 n =0n =0 n: # vibronic level.

34 |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>←|3/2,3/2,1/2,1> F1 F2

35

36 Ar + Laser CW Ring Dye Laser Computer Etalon Chopper (2KHz) λ/2 PlatePBS PD Calibration System I2I2 50cm ~100mW 1-3 mW Lock- in Experimental Apparatus: Ring Laser & Calibration System LIF resolution (FWHM): ~250MHz LIF accuracy (1σ): ~50MHz to dye amplifier

37  : Hund’s case (a)  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)  J - total angular momentum of the molecule;  N - rotational angular momentum;  K - projection of N onto the molecule-fixed z or a axis;  p =±1 - parity. Notations of Hund’s case (a) and (b)

38 s1s1 s0s0 SEP=s 1 /s 0  I fl DUMP PUMP s1s1 s0s0 SEP=S 1 / S 0 Dump Pump Photolysis Stimulated Emission Pumping (SEP: Pump-Dump)

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

40 SEP Spectrum of CH 3 O *LIF excited by dump laser

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