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

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

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

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

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

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

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

June 18, 2008The University of Illinois8 The First Positive Group (B 3 Π g – A 3 Σ g + ) of N 2 n'' n' 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, – cm -1 diode laser

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

June 18, 2008The University of Illinois10 Spectral Calibration

June 18, 2008The University of Illinois11 Spectral Calibration

June 18, 2008The University of Illinois12 Spectral Calibration 9

June 18, 2008The University of Illinois13 Spectral Calibration

June 18, 2008The University of Illinois14 Spectral Calibration

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

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

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

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, Parameter Our Values Ground State B (79) λ (23) γ x (92) D x (98) Upper State Origin B (79) A (18) λ (52) o (30) p x (26) q x (11) D x (96)

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

June 18, 2008The University of Illinois20 Conclusions and Future Work The cw-CRDS spectra of N 2 + and N 2 * from – 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

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