HIGH RESOLUTION JET COOLED CAVITY RINGDOWN SPECTROSCOPY OF THE A STATE 31

0 BAND OF THE NO3 RADICAL

Terrance J. Codd, Mourad Roudjane

and Terry A. Miller

The Ohio State University

~

Introduction

• Having observed and assigned the 3 fundamental using moderate resolution radiation we would like to obtain a high resolution spectrum of this band to confirm the assignment

• Also, see if the rotational structure indicates the presence of strong JT coupling• In the limit of strong JT coupling the molecule would be

permanently distorted to a lower symmetry geometry• Rotational structure is the best way to observe distortions of

molecular geometry

HR JC-CRDS

CW

CW

Ti:Sa

YAG

20 Hz

YVO 4

Ring

D2 Herriott Type Multipass Cell1st stokes ∼ 1.1 μm ∼ 2 mJ~9.5 atm ~210 MHz FWHM

InGaAsDetector

67 cm

WLM

~7 – 30 MHz FWHM (FT limited)30 – 100 mJ/pulse

IR Beam

9 mm

-HV

• radical densities of 1012 - 1013 molecules/cm3 (10 mm downstream, probed)• rotational temperature of 15 - 30 K• plasma voltage ~ 700 V, I 1 A (~ 400 mA typical), 100 µs length• dc discharge, discharge localized between electrode plates, • increased signal compared to longitudinal geometry

Previous similar slit-jet designs: D.J. Nesbitt group, Chem. Phys. Lett. 258, 207 (1996); R.J. Saykally group, Rev. Sci. Instrum. 67, 410 (1996); T. A. Miller group, Phys. Chem. Chem. Phys. 8, 1682 (2006).

5 cm

5 mm

10 mm

Electrode Electrode

Viton Poppet

Precursor in Buffer Gas

Slit Jet/Discharge

Calibration

• Spectrum is calibrated at each frequency point using a High Finesse WS-7 wavemeter

• This has a 3 accuracy of 60MHz and a precision of 20 MHz

• We compared calibration using the wavemeter to calibration using waterlines and found they differed by 100 MHz

• We experimentally measured the D2 Raman shift to be 2987.277 cm-1 at our conditions

Moderate Resolution Spectrum

• Move to 8750 cm-1 to scan relatively weak parallel band there to confirm the assignment

8600 8800 9000 9200 9400 9600

0

1

2

3

4

5

pp

m

wavenumber

ppm

/pas

s

430

11042

0

310

21042

0

22041

0

12042

0

230

21043

0

12041

0

Spectrum

• Shown is the spectrum of the 310 band

• ~160 lines are resolved

8740 8745 8750 8755 8760 8765

0

5

10

15

20

pp

m/p

ass

wavenumber

ppm

/pas

s

Comparison: 310 v 41

0

8740 8745 8750 8755 8760 8765

-20

-15

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-5

0

5

10

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v3 v4 Shifted

pp

m/p

ass

wavenumber

310

410

ppm

/pas

s

410 data: Ming-Wei Chen Dissertation, 2011

Comparison: 310 v 41

0

8754 8756

-20

-15

-10

-5

0

5

10

15

20

v3 v4 Shifted

pp

m/p

ass

wavenumber

310

410

ppm

/pas

s

410 data: Ming-Wei Chen Dissertation, 2011

Model Used for Simulation

• We used our SPECVIEW software with an oblate symmetric top model with spin-rotation, centrifugal distortion, and NSSW

• We used Hirota’s ground state constants and left them fixed through all fits1

• Fits are performed by iteratively assigning peaks and running a least squares regression of free parameters and then assigning more peaks

• A total of 104 lines were used in the final step of the fit1. Hirota, E. Ishiwata, T. Kawaguchi, K. Fujitake, M. Ohashi, N. Tanaka, I. J. Chem. Phys. 107, 2829 (1997)

Simulation vs. Experiment

• Simulation at 17 K• 104 lines are assigned• Standard Deviation of fit is

158 MHz• Fixed ground state

constants to Hirota’s1

8740 8745 8750 8755 8760 8765

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wavenumber

Excited State Uncertainty

C 0.2082287 5.202E-05

B 0.4299295 9.155E-05Dk 5.2163E-06 1.681E-06Djk -6.0621E-07 1.940E-06Dj -3.2476E-08 9.333E-07

Ebb 0.0165803 2.250E-04

Te 8756.791 1.693E-03

Exp

Sim

1. Hirota, E. Ishiwata, T. Kawaguchi, K. Fujitake, M. Ohashi, N. Tanaka, I. J. Chem. Phys. 107, 2829 (1997)

Simulation vs. Experiment

• Simulation is very good

• For some transitions 1 line is predicted but 2 are observed

• Where a ‘split’ line is in one branch, corresponding peaks can be seen in the other two

• Ground state combination differences confirm that these belong to the same excited state level

8755 8756

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/pas

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wavenumber

8760 8761 8762

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wavenumber

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/pas

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Split Peak Analysis

Split Peaks Frequency Weighted Position Predicted Position Weight-Pred1 8756.297

8756.338 8756.308 8756.313 -0.0048042 8759.787

8759.830 8759.815 8759.808 0.0069593 8761.049

8761.083 8761.072 8761.072 -0.0002454 8761.741

8761.777 8761.751 8761.750 0.0007275 8762.638

8762.661 8762.649 8762.648 0.001059Fit Std Dev in MHz RMS Error in MHz

158 82.70

• Integrated ‘split’ peaks to find weighted position and compared it to the predicted position from the simulation.

Split Lines

• Shown are some of the K = 3 levels and their splitting.J’ N’ K’ Energy levels (cm-1) Diff (cm-1) Diff(MHz)

9/2 4 3 8763.4357 0.04036 12109/2 4 3 8763.3953

11/2 6 3 8772.8158 0.0351 105011/2 6 3 8772.7807

13/2 7 3 8778.8394 0.0286 85713/2 7 3 8778.8108

15/2 7 3 8778.9403 0.0358 107015/2 7 3 8778.9045

21/2 10 3 8802.17618 0.02178 653

21/2 10 3 8802.1544

Conclusions

• We have obtained a high resolution spectrum of the previously unassigned 31

0 band of the A state of NO3

• We have analyzed this spectrum using an oblate symmetric top model

• The rotational structure does not indicate the presence of strong JT coupling

• Several excited state rotational levels are split. This could be caused by perturbations from dark vibronic levels

~

Acknowledgements

• Terry Miller

• Miller Group• Neal Kline• Rabi Chhantyal-Pun• Mourad Roudjane• Takashige Fujiwara• Dianping Sun• Ming-Wei Chen

• NSF - $$$

• You for your attention!Currently at University of Illinois Urbana-Champaign