3C Sugars in Interstellar Hot Cores? The Laboratory Rotational Spectroscopy of and Observational...

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 stateb = 1.8 Dsingly 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• Previously unpublished microwave work now in press: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 GHzb = 1.767 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 meteoriteCooper et al. (Nature 414, 2001)

UV

Hot Core

complex organics

T (gas) = 200 - 1000 K

~1016 cm

T (dust) ~90 K~90 K ~60 K~60 K ~45 K~45 K ~20 K~20 K

SiO

H2O, CH3OH, NH3

H2S

CH3CN

~5x1017 cm

H2O ice

CO2

CON2

O2

iceCO2

icetrappedCO

CH3OHice

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.

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 ReactionsCharnley, 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

Mixer

Mixer Amp

Switch

PINDiode

PINDiode

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

DHA 2 1 2 1 0 1

15006.7695 MHz

Flygare Spectra of DHA Transition Frequency (MHz)

1 1 1 0 0 0 11536.4474

2 1 2 1 0 1 15006.7695

5 0 5 4 1 4 12302.5023

5 1 4 5 0 5 10540.6400

6 0 6 5 1 5 16596.6445

6 1 5 6 0 6 11731.7461

DHA 1 1 1 0 0 0

11536.4474 MHz

Laboratory Work: 2. Caltech and JPL Millimeter and Submillimeter

Flow Cell Spectrometers

Frequency Synthesizer

Lock In Amp.

SourceFlow 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

10185

7916

5626

3376

1107

-1163

-3433

-5702

-7972

112000 112800 113600 114400 115200 116000 116800 117600 118400 119300 120000

Frequency (MHz)

Transition Frequency (MHz)

31 2 30 30 1 29 112558.8289

15 4 11 14 3 12 112580.2057

41 5 36 40 6 35 112590.8853

54 7 48 54 6 49 112600.2144

32 0 32 31 1 31 112612.5095

32 1 32 31 0 31 112636.6087

Parameter 0

1

2

3

Lines Assigned 1256 457 292 239

Energy (cm-1) 0 93 147 150

J max 104 86 70 72

Ka max 23 13 10 13

A 9801.29720( 37) 9764.47769(145) 9701.6815( 44) 9662.11405(274)

B 2051.525463( 84) 2049.846447(286) 2051.54944( 42) 2050.02125( 44)

C 1735.164761( 87) 1736.322042(255) 1737.92890( 35) 1739.41896( 36)

J 0.1823549(102)E-03 0.183262( 35)E-03 0.184902( 59)E-03 0.187034( 61)E-03

JK 0.657431( 99)E-03 0.84808( 44)E-03 0.50435( 98)E-03 0.60889( 81)E-03

K 5.36997( 58)E-03 5.4587( 82)E-03 3.507( 39)E-03 7.1326(190)E-03

J 0.02767141(203)E-03 0.0274030(148)E-03 0.0274835(281)E-03 0.0265713(293)E-03

K 0.569369(157)E-03 0.64404(107)E-03 0.35858(199)E-03 0.31770(214)E-03

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 ~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.

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!

The Difficulty with Double Sideband Observing of Sagittarius B2(N-LMH)

+=

Image sideband

Frequency sideband

Observed Double Sideband Spectrum

desired line position

desired line position

Spectra from Nummelin et al. (ApJ Supp. Series 117, 1998)

Detection of DHA in Sgr B2(N-LMH)?!

CH3CHO (LSB)

No frequency offset, 50 MHz AOS

61 4 58 60 3 57

Frequency offset, 500 MHz AOS

61 4 58 60 3 5715 11 5 14 10 4

60 5 56 59 4 55

67 3 64 66 4 63

Determination of Trot and Column Density (N)via a Rotation Diagram

The integrated intensity of a transition u l is:The integrated intensity of a transition u l is:

Therefore:Therefore:

So a plot of So a plot of versus E versus Euu yields a line yields a line

withwith slope = -1/Tslope = -1/Trotrot and y-intercept = and y-intercept =

19

20

21

22

23

24

25

0 100 200 300 400 500 600

Eu (K)

ln [

8pk

2 IT

mbd

v/h

c3 Ag

]

Trot = 182 K

N = 2.45E15 cm -2

Rotation Diagram for DHA

Other Observational ToolsThe 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 < 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 < 1013 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 13C 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 NAG5-8822

• The NASA SARA program, grant number NAG5-11423