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Hot temperature line lists for metal hydrides
Maire Gorman*, Lorenzo Lodi, Paul C. Leyand, Christian Hill, Sergey N. Yurchenko and Jonathan Tennyson
University College London, Dept of Physics & Astronomy, Gower Street, London WC1E 6BT, UK
*m.gorman.12@ucl.ac.uk

The Exomol project
Exomol project [1]: molecular line lists for spectral characterisation and simulation of astrophysical enviroments for T < 3500 K. · About 30 molecules considered including diatomic metal hydrides (AlH, MgH, NaH, NiH, CrH, TiH, ScH) and oxides (VO, AlO, MgO, TiO).

Transition-metal hydrides
· Forth-row transition metals are fairly abundant, especially Fe and Ni.

Chromium Hydride
· Pivotal role in classification of L type brown dwarfs[7]. · Lines of the A 6+ X 6 + transition system at 8611 е and spanning 10,000 to 6000 е identified in observations of large sunspots [811]. · Pavlenko et al [12] have demonstrated that the A6+ X6+ band of CrH and CrD could feasilibly used for a `deuterium test'[13] which would facilitae the classificaiton of astrophysical objects into planets, brown dwarfs and main-sequence starts. · There are at least 21 low-lying electronic states (up to 20 000 cm-1) in CrH.

Theoretical approach
· Calculations using MRCI (multireference configuration interaction). · Spectroscopy of systems containing transition metals (open d shells) is very challenging and this is the firstever ab initio attempt at producing line lists for these systems. · We account for relativistic effects, basis set extrapolation, spin orbit couplings, homogenous and heterogenous couplings due to angular momentum. · Our group developed the program DUO to solve the coupled problem by expansion in Hund's case (a) basis functions. · Very many low-lying energy levels due to near-degeneracies in atomic d shell great difficulties in ab initio treatment.

Nickel Hydride
· NiH is commonest nickelbearing molecule in cool stellar atmospheres [2]. · NiH lines identified in sunspot spectra around 15 500 cm-1 over 40 years ago [3]. · Knowledge of 58NiH/60NiH isotopologue ratio in stellar spectra could be used to test models of supernovae and star formation. · We focus initially on the three lowest lying electronic terms 2, 2 and 2, which are rather well characterized [4,5,6].
References
[1] J. Tennyson and S.N. Yurchenko, Mon. Not. R. Astron. Soc. 425, 21 (2012) See also www.exomol.com. [2] T. Tsuji, Astron. Astrophys. 23, 411 (1973). [3] D. L. Lambert and E. A. Mallia, Mon. Not. R. Astron. Soc. 151, 437 (1971). [4] J. A. Gray, M. Li, T. Nelis and R.W. Field, J. Chem. Phys. 95, 7164 (1991) [5] C.M. Marian, Ber. Busenges. Phys. Chem. 99, 254 (1995) [6] R. Vallon et al, Astroph. J. 696, 172 (2009) [7] J. D. Kirkpatrick et al, ApJ, 519, 802 (1999) [8] B. Kleman,U. Uhler, CaJPh, 37, 537 (1959) [9] O. Engvold, H. Woehl, J. W. Brault, A&AS, 42, 209 (1980) [10] H.N. Russell, I.S. Bowen, ApJ, 69, 196(1929) [11] H.N. Russell, C.E. Moore, Trans. AM. Philos. Soc, 34, 113(1944) [12] Ya. V. Pavlenko, MNRSA, , 386, 3, 13338 (2008)

Main-group-metal hydrides
· AlH is of importance because of high cosmic abundance of aluminium (8· 104 in the relative scale where abundance(Si)=106). Detected in Mtype and S-type stars and in sunspots. · MgH is important in stellar atmospheric models and is well documented in stellar spectra through observation of the transitions A 2 X 2+ and B' 2+ X 2+. MgH spectra used for determination of Mg and H isotopic ratio in stars and to place constraints on temperature, surface gravity and metal abundance. · Molecules containing main-group (non-transition) metals are relatively straightforward to treat ab initio. · Work on accurate line lists for AlH, MgH as well as NaH is in progress.

· The line list is in an advanced stage and will be ready soon.

[13] G. Chabrier et al, ApJ, 542, 1, 464 (2000)