Theoretical studies on hydrogen activation by iridium dimers

The basic and fundamental mechanisms governing the catalytic reaction of small iridium clusters with H-2 are presented here with the purpose to determine its behavior in hydrogenation reactions. The iridium dimer's lowest states in interaction with H-2 potential energy surface were obtained using ab initio multiconfigurational self-consistent-field calculations (MC-SCF), with relativististic pseudopotentials. The electronic correlation contribution was included by configurations interaction (CI) calculations, which considered a variational part plus a second-order perturbative part. The Ir-2 + H-2 reactions were developed in the C-2v symmetry. The Ir-2's five lowest electronic states were determined, (5)Pi g(,) (3)Pi(g), (1)Sigma(g)(+), ( 3)Sigma(u)(+), and (5)Sigma(g), and studied when reacted with H-2. It was found that the iridium dimer, in these five states, might capture and break the H-H bond, spontaneously in certain cases and after surmounting activation barriers in other cases. (C) 1998 John Wiley & Sons, Inc.