High-Resolution Spectroscopy of the ν16 Band of 1,3,5-Trioxane

Bradley M. Gibson and Nicole KoeppenDepartment of Chemistry, University of Illinois at Urbana-ChampaignBenjamin J. McCall Departments of Chemistry and Astronomy, University of Illinois at Urbana-Champaign

Outline

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1. Motivations2. Previous Work3. Spectrometer Design

a) CRDS Overviewb) Optical Layout

4. Observed Spectra5. Future Work

Figure from: M. Kobayashi et al., “Vibrational Spectra of Trioxane and Trioxane-d6” J. Chem. Phys. 44, 922 (1966)

Why study trioxane?

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• C3v symmetry, chair conformation• Only one rotationally-resolved band

observed• 220 km/mol band at 1178 cm-1

• Strong band would be useful for characterizing newlydeveloped equipment

Figure from: J-F. Henninot et al., “The Infrared Spectrum of Trioxane in a Supersonic Slit Jet”. J. Mol. Spect. 152, 62 (1992)

Previous Studies

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• Numerous low-res vibrational spectra, including Kobayashi et al. in 1965

• Microwave spectrum observed by Oka et al. in 1963• Only one rotationally-resolved spectrum, ν17 by Henninot et al.

in 1992

How does CRDS work?

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AOMLaser PiezoPo

wer

Time

How does CRDS work?

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AOMLaser PiezoPo

wer

Time

How does CRDS work?

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AOMLaser PiezoPo

wer

Time

Cavity on-resonance

How does CRDS work?

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AOMLaser PiezoPo

wer

Time

AOM switched off

How does CRDS work?

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AOMLaser Piezo

Pow

er

Time

• Cavity enhanced sensitivity• No noise from laser power

fluctuation

Spectrometer Layout

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EC-QCL

Fresnel Rhomb

Wavemeter

SO2 Cell

PolarizerCavity

AOM

Figure generated using PGopher

What do we expect to see?

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1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184Wavenumber/cm-1

0.0

0.5

1.0

1.5

2.0

2.5

Nor

mal

ized

Inte

nsity

/ cm

-1

What did we see?

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500

450

400

350

Loss

-Per

-Pas

s (p

pm)

1186118411821180117811761174

Frequency (cm-1

)

What did we see?

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430

420

410

400

390

380

370

360

Loss

-Per

-Pas

s (p

pm)

1180.21180.01179.81179.6

Frequency (cm-1

)

Are the spectra reproducible?

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500

450

400

350

300

Loss

-Per

-Pas

s (p

pm)

1179.21179.01178.81178.6

Frequency (cm-1

)

Peak positions vary by approximately ±150 MHz

What’s causing the uncertainty?

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1180.040

1180.035

1180.030

1180.025Freq

uenc

y (c

m-1

)

5004003002001000

Time (s)

~131 MHz St.Dev.

Figure generated using PGopher

What resolution do we need?

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1178.0 1178.2 1178.4 1178.6 1178.8 1179.0 1179.2 1179.4 1179.6 1179.8 1180.0Wavenumber/cm-1

0.1

0.2

0.3

0.4

0.5

0.6

Nor

mal

ized

Inte

nsity

/ cm

-1

Simulation convolved with 150 MHz gaussian

Figure generated using PGopher

What resolution do we need?

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1178.0 1178.2 1178.4 1178.6 1178.8 1179.0 1179.2 1179.4 1179.6 1179.8 1180.0Wavenumber/cm-1

0

1

2

3

Nor

mal

ized

Inte

nsity

/ cm

-1

Simulated with 30 MHz resolution – resolved!

Is our locked EC-QCL sufficient?

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392

390

388

386

384

382Loss

-Per

-Pas

s (p

pm)

50403020100

Relative Frequency (MHz)

Feature <10 MHz (approx) resolved!

Wikimedia CommonsFigures from: B.M. Gibson et al., “Development of a Sheath-Flow Supercritical Fluid Source for Vaporization of Nonvolatiles

at Moderate Temperatures”. 68th ISMS, 2013

What’s next?

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• Finish stabilizing EC-QCL• Re-acquire spectrum with better stability• Fit spectrum

• New experiments:• Cyanuric Acid• Supercritical Fluid Source

Acknowledgements

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