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Continuous-wave Cavity Ringdown Study of the First Positive Band System of N 2 *

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 ‡ Joshua P. DiGangi * Brian A. Tom Benjamin J. McCall. Departments of Chemistry and Astronomy,

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Continuous-wave Cavity Ringdown Study of the First Positive Band System of N 2 *

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  1. Continuous-wave Cavity Ringdown Study of the First Positive Band System of N2* Brett A. McGuire Susanna L. Widicus Weaver† Michael Wiczer BogdanNegru‡ 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 The University of Illinois

  2. Outline • Motivations • Practical • Scientific • Background • Experimental Details • Previous Work • Spectral Calibration • Mode Hops • Frequency Determination • Assignments • Difficulties • Progress and Molecular Constants • Conclusions and Future Work The University of Illinois

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

  4. Outline • Motivations • Practical • Scientific • Background • Experimental Details • Previous Work • Spectral Calibration • Mode Hops • Frequency Determination • Assignments • Difficulties • Progress and Molecular Constants • Conclusions and Future Work The University of Illinois

  5. Experimental Setup Ar/N2 Discharge 3100 V, 70mA The University of Illinois

  6. CW Cavity Ringdown Spectroscopy (cw-CRDS) Laser AOM R ≥ 99.99% The University of Illinois

  7. Needles in the Haystack The University of Illinois

  8. The First Positive Group (B3Πg – A3Σg+) of N2 First observed in the visible by Deslandres in 1902 (C. R. Society, Paris, 134) Calculated Experimental 10200 – 10600 cm-1 diode laser Adapted from Dieke & Heath Johns Hopkins Spec. Report 17, 1959 & Roux & Michaud J. Mol. Spec. 97, 253, 1983. The University of Illinois

  9. Outline • Motivations • Practical • Scientific • Background • Experimental Details • Previous Work • Spectral Calibration • Mode Hops • Frequency Determination • Assignments • Difficulties • Progress and Molecular Constants • Conclusions and Future Work The University of Illinois

  10. Spectral Calibration The University of Illinois

  11. Spectral Calibration The University of Illinois

  12. Spectral Calibration 9 MODE HOPS The University of Illinois

  13. Spectral Calibration The University of Illinois

  14. Spectral Calibration The University of Illinois

  15. αmin = 5 x 10-10 cm-1 0.03 cm-1 Concatenated Spectra The University of Illinois

  16. Outline • Motivations • Practical • Scientific • Background • Experimental Details • Previous Work • Spectral Calibration • Mode Hops • Frequency Determination • Assignments • Difficulties • Progress and Molecular Constants • Conclusions and Future Work Today’sAssignment The University of Illinois

  17. Pressure Differentiation N2* N2+ The University of Illinois

  18. PGOPHER, a Program for Simulating Rotational Structure, C. M. Western, University of Bristol, http://pgopher.chm.bris.ac.uk Spectral Parameters 119 Lines assigned with an RMS of 0.01 cm-1 The University of Illinois

  19. A Lot Left To Go… The University of Illinois

  20. Conclusions and Future Work • The cw-CRDS spectra of N2+ and N2* from 10227 – 10590 cm-1 have been acquired • 125 N2+ lines from the 2-1 band of the Meinel system have been assigned and spectral parameters determined.‡ • 119 N2* 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 The University of Illinois

  21. NASA Laboratory Astrophysics 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 Ben McCall Brian Tom NSF CHE ACS Dreyfus UIUC The McCall Group http://bjm.scs.uiuc.edu/ The University of Illinois

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