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

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.

What do we know spectroscopically? Ab initio calculations predict: doubly H-bonded conformer = ground state  b = 1.8 D singly H-bonded conformer ~ 750 cm -1 lowest torsional modes ~ 190 cm -1, 280 cm -1, 285 cm -1 Previously unpublished microwave work now in press: Lovas, Suenram, Plusquellic, and Møllendal (J. Mol.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 GHz  b = D No vibrational work has been done.

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)

UV Hot Core complex organics T (gas) = K ~10 16 cm ~90 K T (dust) ~90 K ~60 K ~45 K ~20 K SiO H 2 O, CH 3 OH, NH 3 H2SH2S CH 3 CN ~5x10 17 cm H 2 O ice CO 2 CO N 2 O 2 ice CO 2 ice trapped CO CH 3 OH ice Schematic of a Hot Core

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. Cronin, J. R., Chang, S. (1993) In: J. M. Greenberg et al (Ed.), The Chemistry of Life’s 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). Key Questions: How far can prebiotic chemistry go in the ISM?? Is a parent body required for prebiotic chemistry to occur?? Possible Prebiotic Species Formation Schemes

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!

Again, no sugars! Gas Phase Reactions Alanine

Laboratory Work: 1. Original Balle-Flygare FTMW Spectrometer Valve Driver Local Oscillator Timing Control Freq. Stabilizer Freq. Standard Master Oscillator Amp Mixer Isolator Mixer Amp Switch PIN Diode PIN Diode Freq. Stabilizer  + 30 MHz m  30 MHz Pump Molecular Nozzle  30 MHz To Computer

The Heated Nozzle heater Sample Holder Top View Cross-Sectional View Ar + DHA Ar wire mesh DHA

DHA MHz Flygare Spectra of DHA Transition Frequency (MHz) DHA MHz

Laboratory Work: 2. Caltech and JPL Millimeter and Submillimeter Flow Cell Spectrometers Frequency Synthesizer Lock In Amp. Source Flow Cell Polarizer Detector To Computer Multiplier Rooftop Reflector Heating required for mm scans (~ 50 °C). Cell contamination a problem due to relatively weak DHA linestrengths. Harmonic contamination for submm scans.

3 mm Flow Cell Spectrum of DHA Frequency (MHz) Transition Frequency (MHz)

Rotational and Centrifugal Distortion Constants for Dihydroxyacetone Energies determined by relative line strengths. Global fit  wave RMS = 135 kHz. ~ 85 % of strong lines (> 2  ) assigned. Additional 4 assignments underway.

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 ~10 15 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 T ~ 90 K Note: Low T reduces partition function considerably, lowers expected detection limits. Similar abundances of complex molecules to Sgr and Orion.

Initial Observational Searches with the Caltech Submillimeter Observatory 10.4 meter dish 230 GHz receiver (strong DHA lines) Predicted detection limits for DHA ~ cm -2 Double sideband system The Susannas at the CSO!

The Difficulty with Double Sideband Observing of Sagittarius B2(N-LMH) + = Image sideband Frequency sideband Observed Double Sideband Spectrum desired line position Spectra from Nummelin et al. (ApJ Supp. Series 117, 1998)

Detection of DHA in Sgr B2(N-LMH)?! CH 3 CHO (LSB) No frequency offset, 50 MHz AOS

Frequency offset, 500 MHz AOS

Determination of T rot and Column Density (N) via a Rotation Diagram The integrated intensity of a transition u l is: Therefore: So a plot of versus E u yields a line withslope = -1/T rot and y-intercept =

Rotation Diagram for DHA

Other Observational Tools The Owen’s 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 < 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 < cm -2

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 13 C isotopomers in natural abundance. 2. Assignment of Higher Vibrational States. 4. Torsional Mode Spectroscopic Measurement: Tunable Far-IR experiments.

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 NAG The NASA SARA program, grant number NAG