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Looking for Titanium in space

Looking for Titanium in space. F. Pauzat, J. Ferré, Y. Ellinger Laboratoire d’Etude Théorique des Milieux Extrêmes. Cet exposé s’appuie sur le travail réalisé au LETMEX dans le cadre du Programme National Physique et Chimie de Milieu Interstellaire. New Interstellar Molecules.

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Looking for Titanium in space

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  1. Looking for Titanium in space F. Pauzat, J. Ferré, Y. Ellinger Laboratoire d’Etude Théorique des Milieux Extrêmes Cet exposé s’appuie sur le travail réalisé au LETMEX dans le cadre du Programme National Physique et Chimie de Milieu Interstellaire

  2. New Interstellar Molecules Laboratory Observations Astro/Geo-physics Computational Chemistry Hunt for molecules : interdisciplinary approach Effet P.Encrenaz ?

  3. 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

  4. Rotational constants in the CnH series • Bo (GHz) Year Be (GHz)Be (GHz)∆Be • observedobservedcalculated« best estimate » • C2H 43.675 1974 43.322 • C3H 11.186 1985 11.067 • C4H 4.75919784.7350 • C55 2.395 1986 2.3732 • C6H 1.3862 1986 1.3757 • C7H 0.87448691997 0.867340.873±0.0020.2% • C8H 0.586670719960.582230.586±0.0010.1% • C9H 0.41327791997 0.409620.412±0.0010.3% • Observations: M. Guélin, J. Cernicharo et al, A&A (1996;1997) • Experiments : P. Thaddeus et al, A&A (1996;1997) • Theory : F. Pauzat, Y. Ellinger, A.D. McLean, Ap. J. (1991)

  5. Rotational constants in the CnO series • Bo (MHz) Be (MHz)∆Be • CO 57635.9660(17)58037.220.7% • C2O 11545.5970(7) 11578.94 0.3% • C3O 4810.88638(20)4801.8120.2% • C4O 2351.2625 (2) 2349.3210.1% • C5O 1366.84709(6) 1364.7600.15% • C6O 849.75709(7)849.24310.06% • C7O 572.94105(5)572.65260.05% • C8O 400.64183(8)400.32460.08% • C9O 293.73611(4) 293.75760.01% Experiment : Y. Ohshima, Y. Endo, T. Ogata, J. Chem. Phys, 102, 1493 (1995); JACS, 117, 3593 (1995) Theory : F. Cheikh, F. Pauzat, A&A, 348, 17 (1999)

  6. Cosmic abundances of elements C Si Ti Metals in molecules in Circumstellar environment NaCl NaCN / KCl / AlF AlNC AlCl / MgCN MgNC /

  7. 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)

  8. 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 ?

  9. 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 ?

  10. 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

  11. 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

  12. 3B1 3A” 3A” C2v Cs Cs 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

  13. 3A” 3B1 3A” Cs Cs C2v The lowest electronic states of TiC2 ROHF minimum Trans. State minimum B3LYP minimum Trans. State minimum BH&HLYP minimum 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.

  14. 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

  15. Titanium inmolecular and dust envelope of proto-planetary nebulae HD56126 ?

  16. THE END

  17. Ti Cosmic abundances of atomic species

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