1. MILLIMETRE-WAVE SPECTRUM OF ANTI-13C1 AND 13C2 ISOTOPOLOGUES OF ETHANOL AND APPLICATIONS TO RADIO ASTRONOMY
AURELIA BOUCHEZ, ADAM WALTERS, SANDRINE BOTTINELLI,
IRAP, Université de Toulouse, UPS-OMP, CNRS
HOLGER S. P. MüLLER, MATTHIAS H. ORDU, FRANK LEWEN, MONICA KOERBER, CHRISTIAN P. ENDRES, STEPHAN SCHLEMMER,
I. Physikalisches Institut, Universität zu Köln,
Zülpicher Str. 77, Köln, Germany.
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

2. Context Ethanol CH3CH2OH: - Complex Organic Molecule.
- Prolate asymmetric top with two large amplitude internal motions: one for the methyl and one for the hydroxyl group.
- Two conformations: two symmetrics gauche and one anti.
In the ground vibrational state, the trans substate is the lowest in energy; rotational transitions in this substate are the ones previously observed in the interstellar medium
Souce pictures : J.C. Pearson et al. J. Phys. Chem. (1995), J Mol Spectrosc, 251 (2008)
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

3. M. Ohishi et al., Astrophys J Lett, 446, 1995
Context
Detections:
- W51M (T.J. Millar et al. A & A, 205, 1988, pp. L5–L7)
- Sagittarius B2 (Zuckerman et al. Astrophys J Lett, 196, 1975, pp. L99–L102)
- G (T.J. Millar et al. Mon Not R Astron Soc, 273, 1995, pp. 25–29)
- Orion KL (B.E. Turner Astrophys J Supp Ser, 70, 1989, pp. 539–622; L.M. Ziurys et al. Astrophys J Supp Ser, 89, 1993, pp. 155–187; M. Ohishi et al., Astrophys J Lett, 446, 1995, pp. L43–L46)
- In numerous other massive star forming regions and hot cores
In the low mass protostar IRAS (Bisshop et al, A&A 488, 959–968, 2008)
Observations indicate that ethanol is principally present in hot core regions with gas densities larger than 106 cm−3 and temperatures near or in excess of 100 K.
Ethanol in Orion KL,
M. Ohishi et al., Astrophys J Lett, 446, 1995
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

4. Context H3O+ + C2H4 → C2H5OH2+ + hν C2H5OH2+ + e- → C2H5OH + H
The formation route to ethanol has not been conclusively established
But its large abundance in hot cores suggests a major role for dust chemistry and a subsequent importance in the formation of other complex molecules such as ethers and esters (Charnley et al. 1995).
Possible formation :
- In the gas phase (e.g. Millar et al. 1991):
H3O+ + C2H4 → C2H5OH2+ + hν C2H5OH2+ + e- → C2H5OH + H
- From dissociated carbons as proposed for grain-surface reaction (Bernstein et al. 1995):
CH3•+ CH2O → CH3CH2O• CH3CH2O• + H→ CH3CH2OH
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

5. Interest of isotopologues
Spectra and abundances of isotopologues in the ISM:
Tool in chemical and physical modeling
With the sensitivity of radio-telescopes (ALMA): need spectra of isotopologues:
Identification in surveys
Understand molecular complexity in SFR
Constrain formation routes.
A search for isotopologues of key species in the ISM is limited by the lack of spectroscopic data from laboratory measurements.
That is the case for ethanol.
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

6. Interest of isotopologues
A joint study involving spectroscopy and astrophysics:
Extensive new measurements of 13C-ethanol in the laboratory.
Observations of 13C-ethanol in a molecular rich SFR
- Many transitions of ethanol have been observed, but no investigation of the isotopologues has yet been reported.
CH313CH2OH and 13CH3CH2OH, hereafter 13C1 and 13C2
Search for 13C1- and 13C2-ethanol and determine the respective abundance ratios, to 12C-ethanol to understand the formation of ethanol.
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

7. Interest of isotopologues CH3•+ CH2O → CH3CH2O• CH3CH2O• + H→ CH3CH2OH
Sakai et al. 2010: [ 12C ] / [ 13C1 ] ≠ [ 12C ] / [ 13C2 ] for CCH in TMC-1.
Constrain the formation route: only a reaction with two dissociated carbons could significantly contribute to the formation of this molecule.
Using this method
If we measure a difference in the 13C1/13C2 ratio:
Formation from dissociated carbons; could occur on grains.
CH3•+ CH2O → CH3CH2O• CH3CH2O• + H→ CH3CH2OH
- Otherwise, formation from associated carbons; could occur in the gas-phase.
H3O+ + C2H4 → C2H5OH2+ + hν C2H5OH2+ + e- → C2H5OH + H
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

8. Measurements
Absorption spectra of both 13C isotopologues were recorded at the Universität zu Köln in the millimeter and submillimeter regions. (between 80 and 800 GHz)
Using different experimental setups (solid source, THz, BWO).
Static cell pressures in the range 10–20 μbar were used for all the measurements.
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

9. Measurements Laboratory work 13C1 Culot1 (1969) 13C2 Culot2 (1971)
Frequency range /GHz
Identified lines
238 71
201 11
Max J 36 20 37 7
Max Ka 9 8 2
Parameters in fit 17 3
Accuracy /kHz 50
250 -
RMS of fit /kHz 57 69 23
1J.-P. Culot Ann. Soc. Sci. Bruxelles 83 (1969) 65-95
2J.-P. Culot PhD Thesis (1971)
Info from previous spectrale data used for the fisrt fit
Results are available in Bouchez et al. 2012, JQSRT, Volume 113, Issue 11, July 2012, Pages 1158–1154
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

10. Results 13C1 Asymmetric top : Watson’s S reduction, Ir representation
- 17 Parameters fitted : B, D, H and 2 L
Info from previous spectrale data used for the fisrt fit
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

11. Results 13C1 Predictions at 300 K
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

12. Results 13C2 Asymmetric top : Watson’s S reduction, Ir representation
- Same set of Parameters than 13C1
≤ 1MHz
13C1 ethanol of (a) a single line 121,12–110,11 and
(b) a line showing asymmetric torsional splitting 126,7–125,8.
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

13. Observations
From first investigation in massive SFRs, 13C-ethanol hard to observe or to identify:
Line-density of spectra
Weakness of line intensity
Limit of telescopes sensitivities
IRAM 30m
Sgr B2, source model of A. Belloche, priv. comm.
From existing surveys:
Check the presence of 13C-ethanol isotopologues
Otherwise, determine an upper limit of detection
Obtain telescope time:
- Choose less dense sources
- Reach a very low noise level
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

14. Observations From existing surveys Sources Ratio 12C/13C
Instrument / Telescope
Reference
Sgr B2
≤ 22:1
IRAM 30m
Belloche priv. Comm.
≥ 4:1
Hifi / Herschel
Neill & Bergin priv. Comm.
Orion KL
≤ 10:1
NGC 6334I
Not conclusive
Lis & Emprechtinger priv. Comm.
These ratios are preliminary results and need to be refined
No conclusion on formation pathway
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

15. ______________________ ________________________
Observations
From telescope time:
- Investigation in G with IRAM 30m
- noise level 4mK
But line confusion !!
Lines are blended due to emission from the envelope
Identification and/or determination of an upper limit in progress.
______________
___________________
______________________
________________________
Envelope
_______ ________ ______
Core
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

16. Conclusion and perspectives
Spectroscopic data:
- 13C species are measured for anti conformers
- Accurate predictions are available in the submillimeter wave domain (soon in CDMS)
Astrophysics data:
- Determination of upper limits of detections in different sources
To have a clear detection :
- Minimize line confusion
- Have high spatial resolution, to reduce the beam dilution
ALMA
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH

17. Thanks for your attention
Acknowledgments:
A. Belloche, D. Lis, M. Emprechtinger, J. L. Neill, E. A. Bergin
H. Müller, S. Schlemmer, M. H. Ordu, F. Lewen, M. Koerber and C. P. Endres
Funding :
PCMI (French National Programme)
Deutsche Forschungsgemeinschaft (DFG) in the framework of the collaborative research grant SFB 956.
Bouchez-Giret Aurélia, 67th meeting International Symposium on Molecular Spectroscopy. June 18-22, 2012, Columbus, OH