Continuous-wave Cavity Ringdown Study of the First Positive Band System of N2*

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Continuous-wave Cavity Ringdown Study of the
First Positive Band System of N2
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, Universit
y of Illinois at Urbana-Champaign Department of
Chemistry, Emory University Department of
Chemistry, University of California, Berkeley
Department of Chemistry, University of
Wisconsin-Madison
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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

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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 Its There!
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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

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Experimental Setup
Ar/N2 Discharge 3100 V, 70mA
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CW Cavity Ringdown Spectroscopy (cw-CRDS)
Laser
AOM
R 99.99
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Needles in the Haystack
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The First Positive Group (B3?g A3Sg) 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.
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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

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Spectral Calibration
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Spectral Calibration
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Spectral Calibration
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MODE HOPS
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Spectral Calibration
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Spectral Calibration
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Concatenated Spectra
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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

TodaysAssignment
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Pressure Differentiation
N2
N2
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Spectral Parameters
119 Lines assigned with an RMS of 0.01 cm-1
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A Lot Left To Go
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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
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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/