Potential energy surfaces for Rh–CO, Rh–OC, Ir–CO, and Ir–OC interactions

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The potential energy surfaces for eight low-lying electronic states of the Rh–CO and Rh–OC complexes and of the Ir–CO and Ir–OC complexes have been studied using the complete active space multiconfiguration self-consistent field method followed by the multireference singles+doubles configuration interaction calculations which included up to 1.6 million configurations. In addition, spin–orbit effects are included through the relativistic configuration interaction method for the Ir–CO complex. It is found that the Rh(2F) and Ir(2F) states react spontaneously with CO to form stable RhCO and IrCO molecules in which the 2Δ ground states are 42.4 and 75.1 kcal/mol more stable than Rh(2F)+CO(1Σ+) and Ir(2F)+CO(1Σ+) states, respectively, in the absence of spin–orbit effects. The RhOC and IrOC complexes in the 2Δ states were found to be less stable than Rh(4F)+CO(1Σ+) and Ir(4F)+CO(1Σ+), respectively. The nature of the chemical bond is discussed in terms of the wave function composition, and the electronic population analysis.