Extensive relativistic calculations on the palladium hydride molecule

Abstract

The lower states of the PdH molecule have been studied with different relativistic methods. At the spin-free level, relativistic effects are shown to be crucial for a proper description of the molecule. PdH is shown to be a single-configuration molecule, but the configuration interaction (CI) results are highly sensitive to the choice of orbital basis. Spin–orbit interaction has been included through spin–orbit CI theory based on the second order Douglas–Kroll operator and through fully relativistic CI calculations based on the Dirac–Coulomb Hamiltonian. The results are in good agreement, but requires a proper choice of orbital basis in the spin–orbit CI calculation to ensure a balanced description of all ΛΣ states coupled by spin–orbit interaction.

Ab initio calculations on low‐lying electronic states of PdH

“…Our results for the three lowest‐lying states are in good agreement with previous theoretical studies . Sjøvell et al used CASSCF followed by MRCISD calculations to obtain electronic energies and bond distances, and finally spin‐orbit correction was added using CASSCF wavefunctions. Their computational method was very similar to the one used here and thus similar results are expected.…”

“…For example, our ab initio values for r e and ω e are 1.522 Å and 2036.2 cm −1 , which differ from experimental values by 0.007 Å and 20.2 cm −1 , respectively. These values are also consistent with previous theoretical studies . The dissociation energy of PdH has been estimated by Tolbert and Beauchamp using mass spectrometric experiments, resulting in D 0 = 56 ± 6 kcal/mol.…”

“…Several theoretical investigations have been carried out on PdH for the ground state (X 2 Σ + ) and two low‐lying excited electronic states (1 2 Δ, 1 2 Π) . Balasubramanian et al calculated potential energy curves using the MRCI method with and without including spin‐orbit interaction.…”

“…They calculated spectroscopic constants and compared them with the available experimental data. Sjøvoll et al studied three low‐lying states of PdH molecule with different relativistic methods, and their results pointed to the crucial role of relativistic effects at the spin‐free level and a proper choice of orbital basis in the spin‐orbit CI calculations.…”

Four-Component Electronic Structure Methods for Molecules

“…Upon reduction to non-relativistic form [37,[64][65][66][67]] through a Foldy-Wouthuysen transformation one finds that the relativistic operator contains for instance spin-own orbit inter action in addition to the instantaneous Coulomb interaction.…”