“…Because of their low-lying metastable singlet states, molecules of these groups are of interest as energy carriers or reactants in chemical systems. During the last few years, a number of new b-X, a-X, and X 2 -X 1 transitions have been observed in Fourier transform emission and LIF studies (2)(3)(4)(5)(6)(7)(8), so that the X 3 ⌺ Ϫ (X 1 0 ϩ , X 2 1), a 1 ⌬(a2), and b 1 ⌺ ϩ (b0 ϩ ) states are now known for most of the 25 species. In parallel, ab initio SCF-CI calculations employing relativistic effective core potentials have been carried out for some of the heavy atom-containing molecules, and spin-orbit energy levels, vibrational constants, and bond lengths of the low-lying states as well as radiative lifetimes and transition probabilities of electric and magnetic dipole transitions have been predicted (9 -14).…”