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

June 18, 2008June 18, 2008 The University of IllinoisThe University of Illinois 1

Continuous-wave Cavity Ringdown Study of the First Continuous-wave Cavity Ringdown Study of the First Positive Band System of NPositive Band System of N22

**

Brett A. McGuireBrett A. McGuireSusanna L. Widicus WeaverSusanna L. Widicus Weaver††

Michael WiczerMichael WiczerBogdan NegruBogdan Negru‡

Joshua P. DiGangi*Joshua P. DiGangi*Brian A. TomBrian A. Tom

Benjamin J. McCallBenjamin 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


OutlineOutline Motivations

Practical Scientific

BackgroundBackground Experimental DetailsExperimental Details Previous WorkPrevious Work

Spectral CalibrationSpectral Calibration Mode HopsMode Hops Frequency DeterminationFrequency Determination

AssignmentsAssignments DifficultiesDifficulties Progress and Molecular ConstantsProgress and Molecular Constants

Conclusions and Future WorkConclusions and Future Work


MotivationsMotivations

PracticalPractical Stepping Stone for Ringdown ExperimentsStepping Stone for Ringdown Experiments

Software SuiteSoftware Suite Hardware and opticsHardware and optics Fundamental TechniquesFundamental Techniques

Demonstrates Need for Ion/Neutral DiscriminationDemonstrates Need for Ion/Neutral Discrimination Motivation for SCRIBESMotivation for SCRIBES

ScientificScientific Unobserved/unassigned bandsUnobserved/unassigned bands

BecauseIt’s

There!

WG10 – Andrew Mills


OutlineOutline MotivationsMotivations

PracticalPractical ScientificScientific

Background Experimental Details Previous Work





Experimental SetupExperimental Setup

Ar/N2 Discharge

3100 V, 70mA


CW Cavity Ringdown Spectroscopy (cw-CRDS)CW Cavity Ringdown Spectroscopy (cw-CRDS)

Laser AOM

R ≥ 99.99%


Needles in the HaystackNeedles in the Haystack


The First Positive Group (BThe First Positive Group (B33ΠΠgg – A – A33ΣΣgg++) of N) of N22

n''n'

0 1 2 3 4 5 6 7 8 9

0 9512 8079 6674 5297 3947 2625 1332

1 11217 9784 8379 7002 5652 4331 3037 1772 535

2 12894 11461 10056 8678 7329 6007 4713 3448 2212 1004

3 14540 13108 11703 10326 8976 7654 6361 5096 3859 2681

4 16160 14727 13321 11944 10594 9273 7979 6714 5477 4270

5 17749 16316 14911 13513 12184 10862 9668 8303 7067 5859

6 19309 17876 16471 16093 14742 12422 11129 9862 8627 7419

7 20840 19407 18002 16625 16274 13963 12660 11395 10158 8960

8 20909 19504 18126 16777 16455 14161 12896 11670 10462

9 20976 19599 18249 26927 16612 14369 13132 11924

10 21041 19692 18310 17076 16811 14575 13307

11 21105 19873 18489 17224 15988 14780

12 21166 19873 18607 17370 16163

First observed in the First observed in the visible by Deslandres in visible by Deslandres in

19021902(C. R. Society, Paris, 134)(C. R. Society, Paris, 134)

CalculatedExperimental

Adapted from Dieke & Heath Johns Hopkins Spec. Report 17, 1959& Roux & Michaud J. Mol. Spec. 97, 253, 1983.

10200 – 10600 cm-1 diode laser




BackgroundBackground Experimental DetailsExperimental Details Previous Work Previous Work

Spectral Calibration Mode Hops Frequency Determination




Spectral CalibrationSpectral Calibration


Spectral CalibrationSpectral Calibration9


Concatenated SpectraConcatenated Spectra

0.03 cm-1

αmin = 5 x 10-10 cm-1




BackgroundBackground Experimental DetailsExperimental Details Previous Work Previous Work


Assignments Difficulties Progress and Molecular Constants

Conclusions and Future Work

Today’sToday’sAssignmentAssignment


Pressure DifferentiationPressure Differentiation

N2*

N2+


Spectral ParametersSpectral 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

ParameteParameterr

Our ValuesOur Values

Ground StateGround State

B 1.391092(79)1.391092(79)

λ -1.3152(23)-1.3152(23)

γ x 104 -6.97(92)-6.97(92)

D x 106 6.303(98)6.303(98)

Upper StateUpper State

Origin 10364.126810364.1268

B 1.575317(79)1.575317(79)

A 43.1339(18)43.1339(18)

λ -0.6552(52)-0.6552(52)

o -1.0018(30)-1.0018(30)

p x 102 1.370(26)1.370(26)

q x 104 -1.31(11)-1.31(11)

D x 106 6.705(96)6.705(96)

http://pgopher.chm.bris.ac.uk/


A Lot Left To Go…A Lot Left To Go…



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


AcknowledgementsAcknowledgements

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 CHEACS

DreyfusUIUC

NASA LaboratoryAstrophysics

Brian Tom

Ben McCall

The McCall Group

http://bjm.scs.uiuc.edu/

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

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