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June 18, 2008The University of Illinois 1 Continuous-wave Cavity Ringdown Study of the First Positive Band System of N 2 * Brett A. McGuire Susanna L.

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Presentation on theme: "June 18, 2008The University of Illinois 1 Continuous-wave Cavity Ringdown Study of the First Positive Band System of N 2 * Brett A. McGuire Susanna L."— Presentation transcript:

1 June 18, 2008The University of Illinois 1 Continuous-wave Cavity Ringdown Study of the First Positive Band System of N 2 * Brett A. McGuire Susanna L. Widicus Weaver † Michael Wiczer Bogdan Negru Bogdan Negru ‡ Joshua P. DiGangi* Brian A. Tom Benjamin J. McCall Departments of Chemistry and Astronomy, University of Illinois at Urbana-Champaign † Department of Chemistry, Emory University ‡ Department of Chemistry, University of California, Berkeley *Department of Chemistry, University of Wisconsin-Madison

2 June 18, 2008The University of Illinois2 Outline Motivations Practical Scientific Background Background Experimental Details Experimental Details Previous Work Previous Work Spectral Calibration Spectral Calibration Mode Hops Mode Hops Frequency Determination Frequency Determination Assignments Assignments Difficulties Difficulties Progress and Molecular Constants Progress and Molecular Constants Conclusions and Future Work Conclusions and Future Work

3 June 18, 2008The University of Illinois3 Motivations Practical Practical Stepping Stone for Ringdown Experiments Stepping Stone for Ringdown Experiments Software Suite Software Suite Hardware and optics Hardware and optics Fundamental Techniques Fundamental Techniques Demonstrates Need for Ion/Neutral Discrimination Demonstrates Need for Ion/Neutral Discrimination Motivation for SCRIBES Motivation for SCRIBES Scientific Scientific Unobserved/unassigned bands Unobserved/unassigned bands Because It’s There! WG10 – Andrew Mills

4 June 18, 2008The University of Illinois4 Outline Motivations Motivations Practical Practical Scientific Scientific Background Experimental Details Previous Work Spectral Calibration Spectral Calibration Mode Hops Mode Hops Frequency Determination Frequency Determination Assignments Assignments Difficulties Difficulties Progress and Molecular Constants Progress and Molecular Constants Conclusions and Future Work Conclusions and Future Work

5 June 18, 2008The University of Illinois5 Experimental Setup Ar/N 2 Discharge 3100 V, 70mA

6 June 18, 2008The University of Illinois6 CW Cavity Ringdown Spectroscopy (cw-CRDS) Laser AOM R ≥ 99.99%

7 June 18, 2008The University of Illinois7 Needles in the Haystack

8 June 18, 2008The University of Illinois8 The First Positive Group (B 3 Π g – A 3 Σ g + ) of N 2 n'' n' 0123456789 09512807966745297394726251332 1112179784837970025652433130371772535 21289411461100568678732960074713344822121004 314540131081170310326897676546361509638592681 4161601472713321119441059492737979671454774270 51774916316149111351312184108629668830370675859 619309178761647116093147421242211129986286277419 72084019407180021662516274139631266011395101588960 8209091950418126167771645514161128961167010462 92097619599182492692716612143691313211924 1021041196921831017076168111457513307 11211051987318489172241598814780 122116619873186071737016163 First observed in the visible by Deslandres in 1902 (C. R. Society, Paris, 134) Calculated Experimental Adapted from Dieke & Heath Johns Hopkins Spec. Report 17, 1959 & Roux & Michaud J. Mol. Spec. 97, 253, 1983. 10200 – 10600 cm -1 diode laser

9 June 18, 2008The University of Illinois9 Outline Motivations Motivations Practical Practical Scientific Scientific Background Background Experimental Details Experimental Details Previous Work Previous Work Spectral Calibration Mode Hops Frequency Determination Assignments Assignments Difficulties Difficulties Progress and Molecular Constants Progress and Molecular Constants Conclusions and Future Work Conclusions and Future Work

10 June 18, 2008The University of Illinois10 Spectral Calibration

11 June 18, 2008The University of Illinois11 Spectral Calibration

12 June 18, 2008The University of Illinois12 Spectral Calibration 9

13 June 18, 2008The University of Illinois13 Spectral Calibration

14 June 18, 2008The University of Illinois14 Spectral Calibration

15 June 18, 2008The University of Illinois15 Concatenated Spectra 0.03 cm -1 α min = 5 x 10 -10 cm -1

16 June 18, 2008The University of Illinois16 Outline Motivations Motivations Practical Practical Scientific Scientific Background Background Experimental Details Experimental Details Previous Work Previous Work Spectral Calibration Spectral Calibration Mode Hops Mode Hops Frequency Determination Frequency Determination Assignments Difficulties Progress and Molecular Constants Conclusions and Future Work Today’s Assignment

17 June 18, 2008The University of Illinois17 Pressure Differentiation N2*N2* N2+N2+

18 June 18, 2008The University of Illinois18 Spectral Parameters 119 Lines assigned with an RMS of 0.01 cm -1 PGOPHER, a Program for Simulating Rotational Structure, C. M. Western, University of Bristol, http://pgopher.chm.bris.ac.uk http://pgopher.chm.bris.ac.uk Parameter Our Values Ground State B1.391092(79) λ-1.3152(23) γ x 10 4-6.97(92) D x 10 66.303(98) Upper State Origin10364.1268 B1.575317(79) A43.1339(18) λ-0.6552(52) o-1.0018(30) p x 10 21.370(26) q x 10 4-1.31(11) D x 10 66.705(96)

19 June 18, 2008The University of Illinois19 A Lot Left To Go…

20 June 18, 2008The University of Illinois20 Conclusions and Future Work The cw-CRDS spectra of N 2 + and N 2 * from 10227 – 10590 cm -1 have been acquired 125 N 2 + lines from the 2-1 band of the Meinel system have been assigned and spectral parameters determined. ‡ 119 N 2 * lines from the 3-3 band have been assigned and spectral parameters determined. Many of the weaker lines are most likely assignable Nail down the fit, finalize the constants Compare to those from the global fit of Roux et al. † Lines from the 2-2, 4-4, 7-8, and 8-9 bands may also be visible in this region and will be analyzed in future studies. ‡ Widicus Weaver et al., J. Mol. Spec., 249, 2008 † Roux et al., J. Mol. Spec. 97, 1983

21 June 18, 2008The University of Illinois21 Acknowledgements Susanna Widicus Weaver and Ben McCall Former group members Joshua DiGangi, Bogdan Negru, and Michael Wiczer Dr. Colin Western at the University of Bristol for the fitting program PGOPHER NSF CHE ACS Dreyfus UIUC NASA Laboratory Astrophysics Brian Tom Ben McCall The McCall Group http://bjm.scs.uiuc.edu/


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