**GRECP/MRD-CI calculations of the spin-orbit splitting
in**
**the ground state of Tl and of the spectroscopic properties**
**of TlH**

**Authors: A.V.Titov, N.S.Mosyagin, A.B.Alekseyev, R.J.Buenker**
**Comments: 20 pages, latex, no figures, more comutational details
are available at at this http URL**
**Subj-class: Chemical Physics**

** The generalized relativistic effective core
potential (GRECP) approach is employed in**
** the framework of multireference single-
and double-excitation configuration interaction**
** (MRD-CI) method to calculate the spin-orbit
(SO) splitting in the $^2P^o$ ground**
** state of the Tl atom and spectroscopic
constants for the $0^+$ ground state of TlH.**
** The 21-electron GRECP for Tl is used and
the outer core 5s and 5p pseudospinors**
** are frozen with the help of the level shift
technique. The spin-orbit selection scheme**
** with respect to relativistic multireference
states and the corresponding code are**
** developed and applied in the calculations.
In this procedure both correlation and**
** spin-orbit interactions are taken into
account. A [4,4,4,3,2] basis set is optimized for**
** the Tl atom and employed in the TlH calculations.
Very good agreement is found for**
** the equilibrium distance, vibrational frequency,
and dissociation energy of the TlH**
** ground state ($R_e=1.870 \AA, \omega_e=1420
cm^{-1}, D_e=2.049 eV$) as**
** compared with the experimental data ($R_e=1.868
\AA, \omega_e=1391 cm^{-1},**
** D_e=2.06 eV$).**