THEORETICAL-STUDY OF THE ELECTRONIC-STRUCTURE OF THE BA-2 MOLECULE

The electronic structure of Pa-2 has been investigated using a 10-electron relativistic pseudopotential, Configuration interaction with four active electrons and core-polarisation potential. Fine structure has been taken into account through a semiempirical spin-orbit operator, Potential energy curves have been determined for all the molecular states dissociating into Ba(6s(2))+ Ba(6s(2); 6s5d; 6s6p) and spectroscopic constants have been obtained for bound states. Evidence for a doubly excited nature of various excited states is pointed out. The ground state of Pa-2 is found to be weakly bound (D-e = 0.202 eV) at long range (R(c) = 9.22 a(0)) with an harmonic frequency omega(c) = 35 cm(-1). The calculated energy for the transition (2)(1) Pi(g)-X(1) Sigma(g)(+) is found to be in very good agreement with an infrared band observed at 850 nm in the absorption spectrum of Pa-2 isolated in solid matrix. Almost all present results are new for excited states.