Ten low-lying electronic states of Pd3

Multiconfiguration self consistent field (MCSCF) followed by multireference singles plus doubles configuration interaction (MRSDCI) calculations, including up to two million configurations, are carried out on low-lying electronic states of Pd3. In addition, spin-orbit effects are included using a relativistic configuration interaction (RCI) method. There are at least ten low-lying electronic states in the absence of spin-orbit coupling (and more when spin-orbit effects are included) of 1A2, 3B2, 3A1, 1A1, 3A2, 3B1, 5A2, 5B1 symmetry with isosceles triangle structures. The calculated density of states is in accord with the recently observed photoelectron spectrum of Pd/sup -/3. The Pd3 trimer was found to be more stable than the dimer with an atomization energy of 124 kcal/mol in the ground state with respect to the separated Pd(3D) atoms. The Mulliken population analysis of the MRSDCI natural orbitals reveal that the apex atom of the isosceles triangle has a considerably larger s population in comparison to the base atoms, while the base atoms have larger d populations in most of the electronic states. All the electronic states of Pd3 exhibit small hybridization of 5p orbitals of the palladium atoms