Theoretical study of the lowest states of CsH and Cs₂

The 19 lowest states of CsH and the 11 lowest states of Cs 2 have been calculated using a non-empirical relativistic effective core potential considering the caesium atom as a one-electron system. The core-valence polarisation and correlation energy has been included employing a recently developed perturbation treatment. The experimental atomic spectrum of caesium is well reproduced. The calculated energy curves show the remarkable precision of this procedure for the ground-state characteristics. For CsH, R e =4.47 Bohr (experimental 4.71 Bohr), D e =1.80 eV (experimental 1.83 eV), omega e =871 cm -1 (experimental 891 cm -1 ); for Cs 2 , R e =8.75 Bohr (experimental 8.78 Bohr), D e =0.40 eV (experimental 0.45 eV), omega e =41 cm -1 (experimental 42 cm - ). The well-to-well transition energies are in error by less than 400 cm -1 for experimentally known transitions.