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Looking for Titanium in space
F. Pauzat, J. Ferré, Y. Ellinger Laboratoire
dEtude Théorique des Milieux Extrêmes
Cet exposé sappuie sur le travail réalisé au
LETMEX dans le cadre du Programme National
Physique et Chimie de Milieu Interstellaire
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Hunt for molecules interdisciplinary approach
Effet P.Encrenaz ?
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Determination of rotational constants
The final identification of a molecule relies
upon the perfect match of the observed spectrum
with the corresponding terrestrial spectrum of
the same molecule however, numerical
simulation using first principle quantum
calculations may be crucial in determining
theoretical rotational constants.

• Looking for the next member in a n-series
• Quadratic extrapolation
• Limit of with increasing n

• Looking for a unique target
• Correction of individual geometrical parameters
• Transferability of between
  isovalent systems

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Rotational constants in the CnH series
Bo (GHz) Year Be (GHz)
Be (GHz) ?Be observed
observed calculated  best estimate  C2H
43.675 1974 43.322 C3H 11.186
1985 11.067 C4H 4.759
1978 4.7350 C55 2.395 1986
2.3732 C6H 1.3862 1986
1.3757 C7H 0.8744869 1997
0.86734 0.8730.002 0.2 C8H
0.5866707 1996 0.58223
0.5860.001 0.1 C9H 0.4132779
1997 0.40962 0.4120.001 0.3
Observations M. Guélin, J. Cernicharo et
al, AA (19961997) Experiments P. Thaddeus
et al, AA (19961997) Theory F. Pauzat,
Y. Ellinger, A.D. McLean, Ap. J. (1991)
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Rotational constants in the CnO series
Bo (MHz) Be (MHz) ?Be CO
57635.9660(17) 58037.22 0.7 C2O
11545.5970(7) 11578.94 0.3 C3O
4810.88638(20) 4801.812 0.2 C4O
2351.2625 (2) 2349.321 0.1 C5O
1366.84709(6) 1364.760 0.15 C6O
849.75709(7) 849.2431 0.06 C7O
572.94105(5) 572.6526 0.05 C8O
400.64183(8) 400.3246 0.08 C9O
293.73611(4) 293.7576 0.01
Experiment Y. Ohshima, Y. Endo, T. Ogata, J.
Chem. Phys, 102, 1493 (1995) JACS, 117, 3593
(1995) Theory F. Cheikh, F. Pauzat, AA, 348,
17 (1999)
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Cosmic abundances of elements
Ti
C
Si
Metals in molecules in Circumstellar environment
NaCl NaCN /
KCl / AlF AlNC AlCl /
MgCN MgNC /
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Titanium carbide in Circumstellar environment ?
Although the hypothesis of TiC being the carrier
of the 21 µm band was first promising, later
studies suggested that there is not enough TiC to
form the nanocrystals required. Could we find
signatures of smaller species with Ti and
C? TiCH TiC2, TiC2H2 TiCN, TiNC
The emission spectrum from post-AGB object SAO
96709 taken by ISO (top) and TiC nanocrystal
clusters (bottom) adapted from Von Helden et al.
(2000)
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Titanium carbide in Meteorites
Meteorites are known to contain micrometer sized
graphite grains with embedded Titanium carbide
cores which are believed to have served as
heterogeneous nucleation centers for graphite
grain condensation. Other interstellar grains
contain Silicon carbide cores.
Could Titanium behave as Carbon ? as Silicon ?
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Carbon - Silicon - Titanium
C Si Ti
Electronic 2s2,2p2 3s2,3p2
4s2,2d2 Configurations Oxides CO SiO
TiO Dioxides CO2 SiO2 TiO2 Carbides CC SiC
TiC
The smallest clusters ?
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Possible structures of TiC2H2 investigated
3A2
All structures optimized in triplet and singlet
states, for all possible electronic
configurations in C2v, Cs and C1 symmetries
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The lowest electronic states of TiC2H2 (kcal/mol,
GHz, Debye)
Structure State
Energy A B C µ
1A1 3A 3A2
35.6 10.6 0.0
292.640 292.577 34.4850
4.0494 3.6013 8.0988
3.9941 3.5575 6.5585
4.0 3.4 3.3
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Possible structures of TiC2 investigated
Open structures higher in energy
Closed structures more stable
All structures optimized in triplet and singlet
states, for all possible electronic
configurations in C2v, Cs and C1 symmetries
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The lowest electronic states of TiC2
ROHF minimum Trans. State minimum
B3LYP minimum Trans. State minimum BHHLYP mi
nimum Trans. State minimum PW91 minimum Trans.
State minimum CCSD flat potential CASSCF(6,6)
minimum
The energy difference between 3A and 3B1 is very
small and depends on the level of theory. The
series of calculations has not yet been converged
to ascertain the structure Cs or C2v of this
small cluster. Whatever the exact geometry, the
dipole moment is µ 10 Debye.
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The current status of Ti clusters (DFT/B3LYP,
GHz, Debye)
A B C µ
Experiment Theory After scaling on
C3H2 Theory n(m) 16.9 16.1
15.2 12.4 10.7 9.3 6.8 3.36
3.33 I(km/mole) 55 36 117
13 0 65 34 38 55
Theory n(m) 32.1 17.4
5.2 method CASSCF
35.093 34.925 34.318 51.116
32.296 32.330 8.106 8.286
16.746 16.789 6.571 7.130
3.4 3.3 10.4
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Titanium in molecular and dust envelope of
proto-planetary nebulae HD56126 ?
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THE END
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Cosmic abundances of atomic species