Theoretical study on Pd dimer and trimer interaction with the hydrogen molecule

The H₂ interaction with the Pd dimer and trimer were studied using multiconfigurational self-consistent field (MC-SCF) calculations with the 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 Pd₂ first six states: ³Σ⁺_u, ¹Σ⁺_g, ³Π_g, ³Δ_xy, ¹Σ⁺_u, and ³Σ⁺_g. For them, the four geometrical approaches included were the side-on H₂ toward Pd₂, for the hydrogen molecule in and out the Pd dimer plane; the perpendicular end-on H₂ toward Pd₂; and the perpendicular end-on Pd₂ to H₂. The Pd₂ ground state is ³Σ⁺_u, which only captures H₂ in the C_2v end-on approach, softly relaxing the H(SINGLE BOND)H bond. The closed-shell ¹Σ⁺_g captures the H₂ molecule in all the approaches considered: The side-on approach of this state presents deep wells and relaxes the H(SINGLE BOND)H bond, and the end-on approach captures H₂ with a relatively longer H(SINGLE BOND)H distance and also a deep well. The ³Π_g state was the only one which did not capture H₂. For the triangular Pd₃ clusters, H₂ was approached in the C_2v symmetry in and out of the Pd₃ plane. In the triangular case, H₂ was absorbed in both spin states, with deep wells and relaxing the H(SINGLE BOND)H distance. The linear Pd₃ singlet and triplet states capture outside of the Pd₃ and break the H(SINGLE BOND)H bond. © 1997 John Wiley & Sons, Inc.