The nature of the [20.0] 1Sigma+ electronic state of RhB: a multiconfigurational study.

Multiconfigurational second order perturbation theory, with extended atomic basis sets and inclusion of scalar relativistic effects, was employed to investigate the low-lying (1)Sigma(+) electronic states of RhB. The [20.0] (1)Sigma(+) state is represented by a single configuration, mid R:[ellipsis (horizontal)]10sigma(2)11sigma(1)5pi(4)2delta(4)12sigma(1), derived from a single excitation (11sigma-->12sigma) from the ground state, which defines its electronic nature. A new excited state, coined as [9.0] (1)Delta (R(0)=1.786A, DeltaG(12)=792 cm(-1)), located 9221 cm(-1) above the X(1)Sigma(+) state, and described by the |...10sigma(2)11sigma(2)5pi(4)2delta(3)12sigma(1)> electronic configuration, was also identified.