A theoretical study of the low-lying states of the AuSi molecule: An assignment of the excited A and D states

The lowest 42 electronic states of diatomic gas phase gold silicide are calculated by complete active space self-consistent field and second-order multiconfigurational perturbation theory. The scalar relativistic effect is considered by the third-order Douglas-Kroll method and the spin–orbit coupling is treated perturbatively after the spin-free calculations. The ground state of AuSi is confirmed to be the 2Π1/2 state, and the spin–orbit splitting of 2Π1/2 to 2Π3/2 is estimated as 1527 cm−1. From the careful analysis of the potential energy curves and the spectroscopic constants, the experimentally observed A and D excited states are assigned to Ω = 1/2(II) or Ω = 1/2(III) and Ω = 1/2(V) or Ω = 1/2(VI), respectively. © 2002 American Institute of Physics.