THEORETICAL-STUDY ON PD DIMER AND TRIMER INTERACTION WITH THE HYDROGEN MOLECULE

The H-2 interaction with the Pd dimer and trimer were studied using mu lticonfigurational self-consistent field (MC-SCF) calculations with th e relativistic effective core potential (RECP); the correlation energy correction was included in the extended multireference configuration interaction (MRCI), variational and perturbative to second order. Here , we considered the Pd-2 first six states: (3) Sigma(u)(+), (1) Sigma( g)(+), (3) Pi(g), (3) Delta(xy), (1) Sigma(u)(+), and (3) Sigma(g)(+). For them, the four geometrical approaches included were the side-on H -2 toward Pd-2, for the hydrogen molecule in and out the Pd dimer plan e; the perpendicular end-on H-2 toward Pd-2; and the perpendicular end -on Pd-2 to H-2. The Pd-2 ground state is (3) Sigma(u)(+), which only captures H-2 in the C-2v end-on approach, softly relaxing the H-H bond . The closed-shell (1) Sigma(g)(+) captures the H-2 molecule in all th e approaches considered: The side-on approach of this state presents d eep wells and relaxes the H-H bond, and the end-on approach captures H -2 with a relatively longer H-H distance and also a deep well. The (3) Pi(g) state was the only one which did not capture H-2. For the trian gular Pd-3 clusters, H-2 was approached in the C-2 upsilon symmetry in and out of the Pd-3 plane. In the triangular case, H-2 was absorbed i n both spin states, with deep wells and relaxing the H-H distance. The linear Pd-3 singlet and triplet states capture outside of the Pd-3 an d break the H-H bond. (C) 1997 John Wiley & Sons, Inc.