Low-energy spectrum of the thermodynamically stable BaI~2+ dication

摘要

Relativistic effective core potential calculations, including configuration interaction and spin-orbit coupling, are reported for the lowest-lying electronic states of the BaI~2+ dication, and the results are compared with the data for the isovalent CaX~2+ (X=Cl, Br, I) systems studied earlier within the same approach. The X_1 ~2#PI#_3/2 and X_2 ~2#PI#_1/2 states are found to be thermodynamically stable by 0.92 and 0.56 eV, as also is the first excited state, A~2#SIGMA#~+, although its potential curve is crossed at large internuclear distances by a repulsive #OMEGA#=1/2 state. All other low-lying electronic states of CaX~2+ are repulsive. Electric-dipole moments are calculated for the A->X_1, X_2 transitions. The corresponding radiative lifetimes are computed to be: #tau#(A->X_1)=5.0 ms and #tau#(A->X_2)=141 #mu#s (the values given are for v'=0). It is concluded that the most favourable situation for spectroscopic observation of this group of dications occurs for the heavier CaI~2+ and BaI~2+ species because they exhibit the largest A-X_1, X_2 transition energies and highest transition probabilities.