AB-INITIO STUDY OF THE 3 LOWEST-LYING (X(1)SIGMA(+), (3)SIGMA(+), AND (1)SIGMA(+)) ELECTRONIC STATES OF AGF

Ab-initio pseudopotential two-configuration self-consistent field followed by extensive variational and perturbational second order Møller-Plesset multireference configuration interaction calculations using localized molecular orbitals were performed to characterize the structure and adiabatic potential energy curves of the three lowest (X 1Σ+, 3Σ+, and 1Σ+) purely electronic states of the AgF molecule. Spin-orbit interactions were introduced semiempirically in a second step. The very strong coupling of the neutral Ag(4d10 5s1)F(2s22p5) and ionic Ag+(4d95s1)F-(2s22p 6) configurations at rather short internuclear distance for both excited 3,1Σ+ states is responsible for the appearance of very shallow minima, thus leading to a limited number of stable vibrational levels for these excited states as suggested previously for the AO+ state. In contrast with the CuF molecule, where only the ionic configuration Cu+(3,1D)F-(1S) is present in the 3,1Σ+ states, this coupling of ionic and neutral structures in AgF is explained by the relative positions of the valence orbital energies of the neutral Cu and Ag atoms with respect to the 2p level of the halogen atom. These results lead to the assignment of the observed AO+-X 1Σ+ transition as a 1Σ+ - 1Σ+ type transition. The very recently observed αΩ1 and A′Ω1 states are shown to be, respectively, the Ω O- and Ω = 1 spin-orbit components of the 3Σ+ state, which justifies the relabeling of αΩ1 into a αΩO-. The calculated spin-orbit-induced splitting between these two components is in excellent agreement with the observed one after reconsidering spectroscopic data. For all these states the calculated spectroscopic constants are in good agreement with available experimental data. The fourth experimental state, BO+, is probably not correlated with the 3Π valence state as previously suggested but it could rather correspond to a Rydberg ionic state involving the Ag+(4d95p)F-(2s 22p6) structure. © 1995 American Institute of Physics.