AB-INITIO RELATIVISTIC CONFIGURATION-INTERACTION CALCULATIONS OF THE SPECTRUM OF BISMUTH OXIDE - POTENTIAL CURVES AND TRANSITION-PROBABILITIES

A series of configuration interaction calculations employing relativistic effective core potentials including the spin-orbit interaction is reported for the X(1) (2) Pi(1/2) ground and numerous low-lying excited states of the bismuth oxide molecule up to 30 000 cm(-1). Special difficulties connected with the treatment of open-shell systems and double-group irreducible representations are discussed and a feasible computation scheme is developed for dealing with them. The spin-orbit interaction is found to cause a high level of mixing between a variety of low-lying lambda-s states, producing a number of avoided crossings which play a key role in determining the character of the BiO spectrum. A comparison with existing experimental data for both the energy locations and intensities of a large number of band systems indicates that the present calculations are capable of predicting T-e values to an accuracy of 0.1-0.2 eV. Corresponding radiative lifetime results generally agree within a factor of 2, with the best experience occurring for relatively strong transitions. The state which was originally assigned as A (2) Pi(1/2) actually turns out to be dominated by the (4) Pi lambda-s state. The corresponding state with Omega=3/2 has recently been discovered by Fink and Shestakov and is found to undergo a strong nonadiabatic interaction with the X(2) (2) Pi(3/2) state. Two other related states A(3) (4) Pi(1/2) are predicted by the present calculations, but have not yet been verified experimentally. Similarly, the L(1) (2) Phi(7/2) and L(2) (2) Phi(5/2) states found in the present work have also not yet been observed.