Electronic structure and bonding in the Pd2 molecule by all electron a b i n i t i o HF–CI calculations and mass spectrometric measurements

In this study, we present results of all electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of the low-lying electronic states of the Pd2 molecule. The basis set used is of double zeta quality in general, but the 4d orbital has been represented by a triple zeta function. Analysis of basis set superposition errors reveals that the interaction between two Pd atoms in their 1S(4d)10 ground term is nonbonding. Interaction between two Pd atoms in the (4d)9(5s)1 configuration results in formation of a chemical bond almost entirely due to the 5sσg molecular orbital. The six lowest lying states 1Σ+g , 1Γg, 1Σ−u , 3Σ−g , 3Γ+u , and 3Γu are very close in energy, and they all originate from a configuration with a hole in the 4dδ subshell of each of the two atoms. Spin-orbit coupling causes a considerable mixing of the low-lying electronic states. Taking spin-orbit coupling into account reveals the ground state as 0+g with two other states, 5u and 0−u , very close to the ground state. Spectroscopic constants have been derived. Our mass spectrometric measurements combined with our theoretical data yielded the dissociation energy D°0 of Pd2 as 99±15 kJ mol−1. The corresponding heat of formation is 653±15 kJ mol−1.