3C Sugars in Interstellar Hot Cores

1
3C Sugars in Interstellar Hot Cores? The
Laboratory Rotational Spectroscopy of and
Observational Search for Dihydroxyacetone
Susanna L. Widicus August 22, 2003
2
What is Dihydroxyacetone?

• It is the simplest 3C sugar.
• It is a white crystalline powder in dimer form at
  room temperature.
• Its major use is as the active ingredient in
  sunless tanning products.

3
What do we know spectroscopically?

• Ab initio calculations predict
• doubly H-bonded conformer ground state
• mb 1.8 D
• singly H-bonded conformer 750 cm-1
• lowest torsional modes 190 cm-1 , 280 cm-1 ,
  285 cm-1
• Previously unpublished microwave work now in
  press
• Lovas, Suenram, Plusquellic, and Møllendal (J.
  Mol. Spec. 2003)
• ground state assignments from 10 - 20 GHz
• mb 1.767 D
• No vibrational work has been done.

4
Why Dihydroxyacetone?

• Glycolaldehyde detected in Sgr B2(N-LMH)
• Hollis, Lovas, and Jewell (ApJ 540, 2000)
• Acetone detection confirmed in Sgr B2(N-LMH)
• Snyder et al. (ApJ 578, 2002)
• Sugars (DHA) detected in Murchison meteorite
• Cooper et al. (Nature 414, 2001)

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Schematic of a Hot Core
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Possible Prebiotic Species Formation Schemes

• Prebiotic materials form in hot cores and are
  assimilated into meteorites and comets.
• Meteorite or comet parent body forms from cloud
  and prebiotic materials form in situ.

Key Questions How far can prebiotic chemistry
go in the ISM?? Is a parent body required for
prebiotic chemistry to occur??
Cronin, J. R., Chang, S. (1993) In J. M.
Greenberg et al (Ed.), The Chemistry of Lifes
Origins, (Kluwer Academic Publisher),
209. Charnley, S. (1999) Interstellar Organic
Chemistry. In The Proceedings of the Workshop
The Bridge Between the Big Bang and Biology,
(Consiglio Nazionale delle Ricerche, Italy).
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Grain Surface Reactions
Charnley, S. (1999) Interstellar Organic
Chemistry. In The Proceedings of the Workshop
The Bridge Between the Big Bang and Biology,
(Consiglio Nazionale delle Ricerche, Italy).
No sugars!
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Gas Phase Reactions
Again, no sugars!
Alanine
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Laboratory Work 1. Original Balle-Flygare FTMW
Spectrometer
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The Heated Nozzle
Sample Holder Top View
DHA
Cross-Sectional View
Ar DHA
Ar
DHA
wire mesh
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Flygare Spectra of DHA
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Laboratory Work 2. Caltech and JPL Millimeter
and Submillimeter Flow Cell Spectrometers

• Heating required for mm scans ( 50 C).
• Cell contamination a problem due to relatively
  weak DHA linestrengths.
• Harmonic contamination for submm scans.

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3 mm Flow Cell Spectrum of DHA
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Rotational and Centrifugal Distortion Constants
for Dihydroxyacetone
Energies determined by relative line
strengths. Global fit m-wave RMS 135 kHz. 85
of strong lines (gt 2s) assigned. Additional n4
assignments underway.
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Proposed Observational Searches

• Sagittarius B2(N-LMH)
• T 200 K
• Note Boltzmann peak for DHA 250 GHz at this
  T.
• Glycolaldehyde, acetone detected at column
  densities of 1015 cm-2
• Orion Hot Core, Compact Ridge
• T 150 K
• High abundance of many complex molecules.
• W51 e2
• T 120 K
• Similar abundances of complex molecules to Sgr
  and Orion.
• IRAS 16293 - 2422
• T 90 K
• Note Low T reduces partition function
  considerably, lowers
• expected detection limits.
• Similar abundances of complex molecules to Sgr
  and Orion.

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Initial Observational Searches with the Caltech
Submillimeter Observatory

• 10.4 meter dish
• 230 GHz receiver (strong DHA lines)
• Predicted detection limits
• for DHA 1012 cm-2
• Double sideband system

The Susannas at the CSO!
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The Difficulty with Double Sideband Observing of
Sagittarius B2(N-LMH)
desired line position
desired line position

Frequency sideband

Observed Double Sideband Spectrum
Image sideband
Spectra from Nummelin et al. (ApJ Supp. Series
117, 1998)
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Detection of DHA in Sgr B2(N-LMH)?!
CH3CHO (LSB)
No frequency offset, 50 MHz AOS
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Frequency offset, 500 MHz AOS
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(No Transcript)
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Determination of Trot and Column Density (N) via
a Rotation Diagram
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Rotation Diagram for DHA
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Other Observational Tools

• The Owens Valley Radio
• Observatory Millimeter Array
• 6 10 meter dishes
• 3 mm receiver strong lines at
• 112 GHz with expected S/N 6
• Predicted detection limits
• for DHA lt 1013 cm-2
• The Green Bank Telescope
• 110 meter dish
• K and Q band (microwave)
• receivers online in fall 2003
• (lower line confusion limit)
• Predicted detection limits
• for DHA lt 1013 cm-2

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Future Work

• 1. Additional observational work to confirm
  detection
• 3 mm line searches, mapping at OVRO.
• Microwave line searches at GBT.
• 2. Structure Determination
• Isotopic substitution of the hydroxyl protons
  and
• 13C isotopomers in natural abundance.
• 2. Assignment of Higher Vibrational States.
• 4. Torsional Mode Spectroscopic Measurement
• Tunable Far-IR experiments.

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Acknowledgements

• The Blake Group -- especially Geoff!
• Rogier Braakman
• Kathryn Dyl
• Maryam Ali
• Suzanne Bisschop
• The JPL Millimeter and Submillimeter Spectroscopy
  Group
• Brian Drouin
• Tryggvi Emilsson
• The CSO, GBT, and OVRO
• The Goddard Group (Ab Initio Calculations)
• Chip Kent
• The NASA Exobiology program, grant number
  NAG5-8822
• The NASA SARA program, grant number NAG5-11423