The effective valence shell Hamiltonian calculations of spin-orbit splittings in small diatomic hydrides

Spin-orbit coupling splitting in the X(2)Π, A(2)Δ, B(2)Σ(-), C(2)Σ(+), D(2)Σ(+), F(2)Π and a(4)Σ(-) Λ-S states of SiH radical

The potential energy curves (PECs) of eleven Ω states generated from the seven Λ-S bound states of SiH radical are studied in detail using an ab initio quantum chemical method. The PECs are calculated for internuclear separations from about 0.10 to 1.00nm by the CASSCF method, which is followed by the internally contracted MRCI approach with the Davidson modification. The spin-orbit coupling is accounted for with the Breit-Pauli Hamiltonian. Core-valence correlation corrections are included with an aug-cc-pCVTZ basis set. Scalar relativistic correction calculations are made by the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. To discuss the effect of core-electron correlations on the spectroscopic parameters, in particular on the Te, the all-electron basis set, aug-cc-pCVTZ with and without core-electron correlations, is employed to calculate the spin-orbit coupling splitting in the X(2)Π Λ-S state. The all-electron aug-cc-pCVTZ basis set with core-electron correlations is chosen for the present spin-orbit coupling studies. The convergent behavior of present calculations is discussed with respect to the basis set and level of theory. All the PECs are extrapolated to the complete basis set limit. The spectroscopic parameters of seven Λ-S and eleven Ω bound states are evaluated. The splitting energy of X(2)Π Λ-S state is determined as 141.12cm(-1), which agrees well with the recent measurements of 142.896cm(-1). Moreover, other spectroscopic parameters are also in excellent agreement with available measurements. It demonstrates that the spectroscopic parameters of eleven Ω bound states reported here can be expected to be reliable predicted ones.