Ab initio study including spin-orbit effects on the B-X transition of AgI.

The lowest Omega = 0-,0+,1,2 fine-structure potential energy curves arising from the two lowest-lying singlet (X 1Sigma+ and 2 1Sigma+) and the first 3Pi electronic states of AgI were obtained through an effective Hamiltonian; the purely electronic LambdaSSigma energies were used as diagonal elements, which were calculated through extensive complete active space self-consistent field + averaged coupled pair functional calculations, with relativistic effective core potentials and optimized Gaussian basis sets for both atoms. The spin-orbit interactions were included using the Stuttgart effective spin-orbit potentials. For the excited Omega = 0+ states, very strong mixtures were found of the 2 1Sigma+ and 3Pi parents that lead to the fine-structure (0+) single B state (dominated by the 2 1Sigma+ parent at long distance), that explains the B <-- X transitions. The present results also explain the presence of a second long-distance minimum for the B0+ state, experimentally Rydberg-Klein-Rees fitted. These calculations produced, as a byproduct, a new lower-lying Omega = 0+ yet unobserved fine-structure state predicted to exist around 22,000 cm(-1). Our theoretical results are compared and discussed in the light of the experimental data for the B-X transitions in silver halides [J. Chem. Phys. 109, 9831 (1998)].