Transcript 333970x - IDEALS @ Illinois

MILLIMETRE-WAVE SPECTRUM OF
ISOTOPOLOGUES OF ETHANOL FOR
RADIO-ASTRONOMY
Adam Walters,
IRAP, Université de Toulouse, UPS-OMP-CNRS, France.
Mirko Schäfer, Matthias H. Ordu, Frank Lewen,
Stephan Schlemmer, Holger S.P. Müller,
I. Physikalisches Institut, Universität zu Köln, Germany.
Molecular complexity in space
Star-forming regions
Comets & meteorites
NASA / ESA
iso-propyl cyanide, methyl acetate,
ethyl formate, acetamide,
glycoaldehyde,aminoacetonitrile
ethanol, …
Basilicofresco
amino acids
?
Difficulties in studying isotopologues of
complex molecules in the ISM
• Abundance
• Partition function
➡ Need accurate predictions over a
large frequency range from
laboratory spectroscopy. Use
sensitive spectrometers & long pass
cells.
Interest in studying ethanol
• Ethanol
observed in star-forming regions and hot-cores
• Ethanol thought to be formed on grains and to be involved in
formation of more complex species
• More and more broad astrophysical spectral surveys available –
move towards analysing spectra as a whole – need information on all
species present
• Work on D-ethanol complementary to previous on 13C ethanol
• Over-abundance of deuterated complex molecules in star-forming
regions
• Study of isotopologues could give information on formation routes
Interest – multi species analysis
• Ethanol
observed extensively in star-forming regions and hot-cores
Interest - ALMA
Lobe IRAM 30m
180 GHz (14’’)
250 GHz (10’’)
Lobe ALMA
ALMA Band 6 (230 GHz)
(~2’’, baseline = 160m)
• 66 radio telescopes
• high sensitivity
• high spatial resolution
ESO
Background - Formation
Formation mechanism of ethanol in the ISM
not conclusively known
Possible formation routes :
- 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
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Background - Ethanol
Prolate slightly asymmetric top with two large amplitude
internal motions:
Hydroxyl group. Two conformations in the groundstate: gauche
(+ and -) and anti.
Methyl group. Internal rotation
Asymmetric
rotor level
J, Ka, Kc
Gauche 3,27 cm-1
Gauche +
V=0
39,49 cm-1
Anti
J.C. Pearson et al. J. Phys. Chem. (1995), J Mol
Spectrosc, 251 (2008)
Background -Deuterated Ethanol
CH2DCH3OH (s- and a-) CH3CHDOH CH3CH2OD
Background – dataset
Dataset chosen
identification.
for
first
astrophysical
• Anti- conformer (lowest energy)
• Torsional ground state
• Torsional splitting unlikely to be resolved in
astrophysical spectra
• b-type spectra
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Previous measurements
references are given in our publication
(see last slide)
Experimental setup
•Double-pass cell
•Solid-state sources
•Computer control
•Highly user friendly
• These measurements:
35 − 500 GHz
Results – onset of shifts
• Dataset chosen for first astrophysical detection.
• First analysis with standard S-reduction Watson
Hamiltonian and without considering torsion-rotation and
anti-gauche interactions. (SPFIT, SPCAT – H.M. Pickett)
Results – example scan
Results – parameter list
Acknowledgements
• Deutsche Forschungsgemeinschaft (DFG) - collaborative research
grant SFB 956
• CNRS – Programme PCMI France : Programme National de Physique
et Chimie du Milieu Interstellaire
References
 Bouchez et al, Journal of Quantitative
Spectroscopy & Radiative Transfer 113 (2012) 1148–1154
13C-ethanol
D-ethanol  Walters et al, Journal of Molecular
Spectroscopy 314 (2015) 6-12