ROTATIONALLY RESOLVED A2A1 - X2E ELECTRONIC SPECTRA OF

SYMMETRIC METHOXY RADICALS: CH3O AND CD3O (RI08)

MING-WEI CHEN, JINJUN LIU, DMITRY G. MELNIK and TERRY A. MILLER

Laser Spectroscopy FacilityDepartment of ChemistryThe Ohio State University

6/19/2008

~ ~

63rd OSU International Symposium on Molecular Spectroscopy

Outline

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 CH3O and CD3O.

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 CH3O and CD3O.

Global fitting and spectral analysis. Model compounds for other isotopomers.

Summary.

Motivations and Aims

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 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.

Spectroscopy of Methoxy Radicals

~2

1AA

~2

1/2EX~

23/2EX

LIF3

SEP

~2

1/2EX

~2

3/2EX

Microwave1,2

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)

5J. Liu, J. T. Yi, V. Starkursky, and T. A. Miller, 61st International Symposium on Molecular Spectroscopy, TJ04&05 (2006).

3D. E. Powers, M. B. Pushkarsky, and T. A. Miller, J. Chem. Phys. 106, 6863 (1997)

resolution~250MHz

resolution~3GHz

4A. Geers, J. Kappert, F. Temps, and J. W. Wiebrecht, J. Chem. Phys. 101, 3618 (1994)

ΔΣ=0ΔP=0

SEP4

~60 cm-1

LIF5

ΔP=±1ΔΣ=±1

p+1-1

Reflection parity (p): Reflection partity (p):

|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+1-1

21/ 2X E

21A A

23/ 2X E

Rotationally Resolved SEP

Hund’s case (a)

Hund’s case (b)

Experimental Apparatus: Overview

CH3ONO (CD3ONO)/ 1st 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

T0

PMT

SHG

SHG

Frequency reading

Photolysis

Dump

Pump

Q-Switch

Flash Lamp

T0 / GPIB

T0

program

0

11 '

S

SS

synchronizing

Lens

Calibration method Doppler-limited I2

resolution ~0.12cm-1

accuracy ~0.05cm-1

Calibration method Doppler-free I2 +Etalon

resolution ~250MHz

accuracy ~50MHz

SEP Spectra

CH3O CD3O

32892 32894 32896 32898 32900 32902 32904-25

-20

-15

-10

-5

0

5

32894.0 32894.1

-8

-6

-4

-2

0

2

P2b

pumped, moderate-resolution dump

P2a

pumped, moderate-resolution dump

32892 32894 32896 32898 32900 32902 32904-25

-20

-15

-10

-5

0

5

Dep

letio

n R

ate

(%)

32898.6 32898.7 32898.8

Dump Frequency / cm -1

32901.5 32901.6

P2a

+P2b

pumped, high-resolution dump

32838 32840 32842 32844 32846-15

-10

-5

0

5

32838 32840 32842 32844 32846-15

-10

-5

0

5

32838.7 32838.8

-10

-5

0

5

32842.4 32842.5 32844.7 32844.8

P2b

pumped, moderate-resolution dump

Dep

letio

n ra

te (

%)

P2a

pumped, moderate-resolution dump

Dump Frequency / cm -1

P2a

+P2b

pumped, high-resolution dump

|N',J',K',p'> → |J,P,Σ,p>

|0,1/2,0,1> → |3/2,1/2,-1/2,-1>

16420.60 16420.65 16420.70 16420.75 16420.80 16420.85 16420.90

16420.60 16420.65 16420.70 16420.75 16420.80 16420.85 16420.90

16420.60 16420.65 16420.70 16420.75 16420.80 16420.85 16420.90

32841.2 32841.3 32841.4 32841.5 32841.6 32841.7 32841.8

wavenumbers / cm -1

Atlas

Iodine

FWHM~30MHz

EtalonFinesse~10

FSR~477MHz

CD3O SEP

FWHM~250MHz

SEP Results of CH3O

# Pump |J",P", Σ",p "> |N', J', K', p '> |J, P, Σ, p > ΔE / cm-1

1 P1 |3/2,3/2,1/2,-1> |0,1/2,0,1> |1/2,1/2,-1/2,-1> 61.8578

2 P1 |3/2,3/2,1/2,-1> |0,1/2,0,1> |3/2,1/2,-1/2,-1> 64.6635

3 P2a |3/2,3/2,1/2,1> |1,1/2,0,-1> |1/2,1/2,-1/2,1> 61.8393

4 P2a |3/2,3/2,1/2,1> |1,1/2,0,-1> |3/2,1/2,-1/2,1> 64.7106

5 P2b |3/2,3/2,1/2,1> |1,3/2,0,-1> |1/2,1/2,-1/2,1> 61.8411

6 P2b |3/2,3/2,1/2,1> |1,3/2,0,-1> |3/2,1/2,-1/2,1> 64.7070

7 P2b |3/2,3/2,1/2,1> |1,3/2,0,-1> |5/2,1/2,-1/2,1> 69.3856

8 P3 |3/2,3/2,1/2,-1> |2,3/2,0,1> |3/2,1/2,-1/2,-1> 64.6774

9 P4 |1/2,1/2,1/2,-1> |1,1/2,1,1> |3/2,3/2,-1/2,-1> 77.3720

10 P4 |1/2,1/2,1/2,-1> |0,1/2,-1,1> |3/2,3/2,-1/2,-1> 77.3720

11 P4 |1/2,1/2,1/2,1> |1,1/2,1,-1> |3/2,3/2,-1/2,1> 77.3720

12 P4 |1/2,1/2,1/2,1> |0,1/2,-1,-1> |3/2,3/2,-1/2,1> 77.3720

SEPLIFE

P2b

wa

ven

umb

ers

/ cm

-1

P1

P2a

P3

P4

SEP Results of CD3O

# Pump |J",P", Σ",p"> |N', J', K', p'> |J, P, Σ, p> ΔE / cm-1

1 P1 |3/2,3/2,1/2,-1> |0,1/2,0,1> |1/2,1/2,-1/2,-1> 55.0520

2 P1 |3/2,3/2,1/2,-1> |0,1/2,0,1> |3/2,1/2,-1/2,-1> 57.2713

3 P2a |3/2,3/2,1/2,1> |1,1/2,0,-1> |1/2,1/2,-1/2,1> 55.0291

4 P2a |3/2,3/2,1/2,1> |1,1/2,0,-1> |3/2,1/2,-1/2,1> 57.3134

5 P2b |3/2,3/2,1/2,1> |1,3/2,0,-1> |1/2,1/2,-1/2,1> 55.0293

6 P2b |3/2,3/2,1/2,1> |1,3/2,0,-1> |3/2,1/2,-1/2,1> 57.3128

7 P2b |3/2,3/2,1/2,1> |1,3/2,0,-1> |5/2,1/2,-1/2,1> 61.0088

8 P3 |3/2,3/2,1/2,-1> |2,3/2,0,1> |3/2,1/2,-1/2,-1> 57.2715

9 P3 |3/2,3/2,1/2,-1> |2,3/2,0,1> |3/2,1/2,-1/2,-1> 61.0731

10 P4 |3/2,3/2,1/2,-1> |3,5/2,0,1> |5/2,1/2,-1/2,-1> 61.0739

11 P5 |1/2,1/2,1/2,-1> |1,1/2,1,1> |3/2,3/2,-1/2,-1> 63.9904

12 P5 |1/2,1/2,1/2,-1> |0,1/2,-1,1> |3/2,3/2,-1/2,-1> 63.9904

13 P5 |1/2,1/2,1/2,1> |1,1/2,1,-1> |3/2,3/2,-1/2,1> 63.9904

14 P5 |1/2,1/2,1/2,1> |0,1/2,-1,-1> |3/2,3/2,-1/2,1> 63.9904

SEPLIFE

P2b

wa

ven

um

be

rs /

cm-1

P1

P2a

P3P

4

P5

ground state (2E):a

HEFF = HROT + HCOR + HSO + HSR + HJT + HCD

Effective Hamiltonian:

Rotational Hamiltonian

Coriolis interaction

Spin-orbit interaction

Spin-rotation interaction

Jahn-Teller interaction

Centrifugal distortion

excited state (2A1):b,c,d

HEFF = HROT + HCOR + HSR + HCD

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

aζed1,2 = −62.24(17)cm-1

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)

21/ 2X E

23/ 2X E

21A A

aζed = −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

-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>

Global Summary of Data

CH3O CD3O

46 40

118 105

320 Band 101 165

610 Band 77 75

12 14

0.05 0.05

1 1

50 50

70 70

0.04 0.09

3.82 0.35

320 Band 33 40

610 Band 78 36

49 44

microwavea

LIFc

SEPc

SEPc

Standard Deviation of Fitting (σ, MHz)LIFc

extended microwaveb

Transitions involved in Global Fitting

SEPc

microwavea

Experimental Accuracy (σ, MHz)

microwavea

extended microwaveb

extended microwaveb

LIFc

Number of assigned transitions

aCH3O: Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984) ; CD3O: Y. Endo, private communication.bCH3O: T. Momose, Y. Endo, E. Hirota, and T. Shida, J. Chem. Phys. 88, 5338 (1988); CD3O: Y. Endo, private communication.cThis work.

LIF Spectra and Simulations

32960 32965 32970 32975

wavenumbers / cm -1

experimental

simulation

32895 32900 32905 32910

wavenumbers / cm -1

experimental

simulation

CH3O, 320 band CD3O, 32

0 band

SEP Spectra and Simulations

CH3O CD3O

32892 32894 32896 32898 32900 32902 32904-25-20-15-10

-505

32894.0 32894.1

-8

-6

-4

-2

0

2

32894.0 32894.1

P2a

pumped, moderate-resolution dump

32892 32894 32896 32898 32900 32902 32904-25-20-15-10

-505

Dep

letio

n R

ate

(%)

P2b

pumped, moderate-resolution dump

32898.6 32898.7 32898.8 32901.5 32901.6

P2a

+P2b

pumped, high-resolution dump

Simulation

32898.6 32898.7 32898.8

Dump Frequency / cm -132901.5 32901.6

32838 32840 32842 32844 32846 32848-15

-10

-5

0

5

32838 32840 32842 32844 32846 32848-15

-10

-5

0

5

32838.7 32838.8

-10

-5

0

5

32842.4 32842.5 32844.7 32844.8

32838.7 32838.8 32842.4 32842.5 32844.7 32844.8

De

ple

tion

ra

te (

%) P

2b pumped, moderate-resolution dump

P2a

pumped, moderate-resolution dump

P2a

+P2b

pumped, high-resolution dump

Dump Frequency / cm -1

Simulation

A 154960 (570) 160050 (315) 154800 (50) 78391 (23)

B 27931.140 (46) 27929.849 (59) 27930.36 (4) 22194.05 (2)D k 2.11 e 2.11 e 2.11 e 0.39 f

D N 0.7699 (38) 0.76963 (108) 0.7693 (20) 0.4040 (3)

D NK 0.07553 (44) 0.075788 (96) 0.07565 (40) 0.04214 (6)

Aζ t 54330 (270) 52273 (124) 52241 (83) 22293 (24)

η e ζ t 1.82 (92) -0.936 (118) 0.264 (74) 0.713 (39)

η K ζt 131.9 (181) 153.1 (58) 31.6 (145) 16.7 (10)

aζ e d -1865980 (5030) -1873283 (1023) -1843707 (113) -1648372 (101)

a D ζ e d 134 (75) 363 (25) 176 (22) 77 (5)

ε aa -40930 (1700) -36897 (508) -37375 (88) -23097 (71)

ε bc -1428 (66) -1579.4 (160) -1111 (3) -841 (2)

ε 1 -171.670 (38) -171.590 (85) 172.65 (13) 142.09 (15)

ε 2a 2420 (1080) -984 (418) -534 (86) -192 (42)

ε 2b 436 c -172 c -96 c -54 c

h 1 75.446 (178) 76.380 (82) -77.68 (214) -88.71 (10)

h 2 1398 (40) 1280.7 (54) -1326 (3) -847 (1)

h 1N 0 e -0.001848 (298) 0.0011 (8) 0.000899 (4)

h 2N -0.0047 (41) -0.01239 (67) -0.0301 (106) -0.0091 (20)

h 1K 0.2356 (116) -0.644 (85) 2.476 (2139) -0.199 (78)h 2K -0.522 (47) -0.519 (17) 0.201 (8) 0.127 (7)h 4 0.00188 (138) -0.00038 (29) -0.00120 (45) -0.00009 (34)

microwavea,e+LIFb+SEPb microwavea,e+LIFb+SEPbextended microwaveemicrowavea

CH3O CD3O

Ground State Parameters

Rotational

Spin-Orbit

Coriolis

Centrifugal Distortion

Spin-Rotation

Jahn-Teller

bThis work cFixed to ε2a*(B/A) d2.5σ in parentheseseT. Momose, Y. Endo, E. Hirota, and T. Shida, J. Chem. Phys. 88, 5338 (1988)

aY. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984)

ffixed to CD3F value.gY. Endo, private communication.

Summary

LIF and SEP spectra are taken with both high-resolution (FWHM~250MHz) and high-accuracy (σ~50MHz).

Direct measurement of E1/2 component of the electronic ground state. Spin-orbit splitting ( )

Correction to parity assignments and Jahn-Teller related parameters (ε1, h1, h2…) from the global fitting involving microwave, LIF, and SEP

Available isotope (CH3O, CD3O) 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 E1/2 component of the electronic ground state. Spin-orbit splitting ( )

Correction to parity assignments and Jahn-Teller related parameters (ε1, h1, h2…) from the global fitting involving microwave, LIF, and SEP

Available isotope (CH3O, CD3O) data for isotopic analysis. (RI09)

ea d

AcknowledgementThe 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