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

Hunt for molecules : interdisciplinary approach Computational Chemistry Laboratory New Interstellar Molecules Observations Astro/Geo-physics

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

Bo (GHz) Year Be (GHz) Be (GHz) ∆B e observed observed calculated « best estimate » C 2 H C 3 H C 4 H C C 6 H C 7 H ± % C 8 H ± % C 9 H ± % 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) Rotational constants in the C n H series

Bo (MHz) Be (MHz) ∆B e CO (17) % C 2 O (7) % C 3 O (20) % C 4 O (2) % C 5 O (6) % C 6 O (7) % C 7 O (5) % C 8 O (8) % C 9 O (4) % 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) Rotational constants in the C n O series

Cosmic abundances of elements TiCSi Metals in molecules in Circumstellar environment NaCl NaCN / KCl / AlF AlNC AlCl / MgCN MgNC /

Titanium carbide in Circumstellar environment ? The emission spectrum from post-AGB object SAO taken by ISO (top) and TiC nanocrystal clusters (bottom) adapted from Von Helden et al. (2000) 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 TiC 2, TiC 2 H 2 TiCN, TiNC …

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 ?

Carbon - Silicon - Titanium Electronic …2s 2,2p 2 …3s 2,3p 2 …4s 2,2d 2 Configurations OxidesCOSiOTiO DioxidesCO 2 SiO 2 TiO 2 CarbidesCCSiCTiC C Si Ti The smallest clusters ?

Possible structures of TiC 2 H 2 investigated All structures optimized in triplet and singlet states, for all possible electronic configurations in C 2v, C s and C 1 symmetries 3A23A2

The lowest electronic states of TiC 2 H 2 (kcal/mol, GHz, Debye) Structure State Energy A B C µ 1 A 1 3 A” 3 A

Possible structures of TiC 2 investigated All structures optimized in triplet and singlet states, for all possible electronic configurations in C 2v, C s and C 1 symmetries Open structures higher in energy Closed structures more stable CsCs 3 A” CsCs C 2v 3B13B1

The lowest electronic states of TiC 2 The energy difference between 3 A” and 3 B 1 is very small and depends on the level of theory. The series of calculations has not yet been converged to ascertain the structure C s or C 2v of this small cluster. Whatever the exact geometry, the dipole moment is µ ~ 10 Debye. ROHFminimumTrans. Stateminimum B3LYPminimumTrans. Stateminimum BH&HLYPminimumTrans. Stateminimum PW91minimumTrans. Stateminimum CCSDflat potential CASSCF(6,6)minimum C 2v 3B13B1 CsCs 3 A” CsCs

The current status of Ti clusters ( DFT/B3LYP, GHz, Debye) Experiment: Theory: After scaling on C 3 H 2 Theory: (  ) 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: (  )* 32.1 ; 17.4 ; 5.2 ; *method: CASSCF A B C µ

Titanium in molecular and dust envelope of proto-planetary nebulae HD56126 ?

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Ti Cosmic abundances of atomic species