Ab Initio Relativistic Effective Core Potential Studies of Metal–Metal and Metal–Hydrogen Bonding in Pd₂, Pt₂, PdH and PtH

The electronic structure of the palladium and platinum homonuclear diatomics (M 2 ) and diatomic hydrides (MH) have been calculated using relativistic effective core potentials in an ab initio multi‐configuration self‐consistent field framework. Calculated spectroscopic properties ( R e and ω e ) of the diatomic hydrides are in close agreement with experiment except for the calculated harmonic force constant in PdH. This latter discrepancy is attributed to inaccuracies in the relative energies of the metal atom in the dissociation limit. The calculated M–M and M–H bond strengths follow the expected trend of the Pt atom forming stronger such bonds than Pd. The metal–hydrogen bonding interaction involves primarily the metal nd orbitals for both Pd and Pt, in contrast to NiH where the main metal bonding orbital has been found to be the 4 s . On the other hand, as in Ni 2 , the Pd–Pd bond is essentially a ( n + 1) s electron pair bond, while the Pt–Pt bond has a substantial 5 d orbital contribution. This quantitative difference between M–M and M–H bonding interactions found for the group VIII transition metals is supported by experimental photoemission energy distribution and difference spectra for the clean metal and hydrogen chemisorbed metal surfaces.