Potential energy curves and interpretation of electronic spectrum of the rhodium monoxide.

Potential energy curves of 17 electronic states of rhodium monoxide (RhO) are calculated by multireference configuration interaction with single and double excitations (MRCISD). The ground state of RhO is determined to be a (4)Sigma(-) state with equilibrium bond length of 1.710 A and harmonic vibrational frequency of 825 cm(-1) at the MRCISD level of theory. It dissociates into Rh((4)F)+O((3)P) with a dissociation energy of 3.77/4.26 eV (MRCISD/MRCISD+Q), which is in agreement with the experimental value of 4.19+/-0.43 eV. Two low-lying excited states a (2)Sigma(-) and b(2)Pi are located at 4152 and 7154 cm(-1) above the ground state. The b(2)Pi with the adjacent (2)Delta, (4)Delta, and (2)Pi(II) states can be strongly coupled via spin-orbit interaction leading to a large splitting between b (2)Pi(3/2)-b (2)Pi(1/2) states with the value of 2422 cm(-1), which is comparable with the experimental value of 2400 cm(-1). Two higher doublets, c(2)Pi and d(2)Pi, have the same dominant configuration, 10sigma(2)11sigma(2)12sigma(1)5pi(4)6pi(3)2delta(3), and their transitions to the ground state, i.e., c(2)Pi-->(4)Sigma(-) and d(2)Pi-->(4)Sigma(-), correspond to the two visible bands of RhO.