MRCI Study of the Electronic Structure and Transition Properties of a Tin Dimer.

The ground and excited states of Sn 2 are calculated using the multireference configuration interaction method combined with Davidson correction (MRCI+Q). The influence of the spin-orbit coupling (SOC) effect on the electronic structure is also considered by the state interaction method of Breit-Pauli Hamiltonian. In the calculations, the potential energy curves and spectroscopic constants of 23 Λ-S states and 31 Ω states of Sn 2 are obtained. The prominent spectral features in the visible region, new constants, and potential energy curves are discussed. The intensity of weak magnetic and quadrupole transitions in the near IR spectra is also calculated. From a computational point of view, we predict that the weak v' (0-2)- v″ (0-5) bands of the magnetic b 1 Σ g,0 + + -X 3 Σ g,1(Ms=±1) - transition may be detected experimentally; the sub-bands (0, 0), (1, 0), and (2, 0) of the a 1 Δ g,2 -X 3 Σ g,1(Ms=±1) - transition also may be observed in experiments since they are not overlapped by the strong electric dipole transition in the same IR region. According to the SOC matrix elements and contributions of the 1 5 Π u0 + , 1 5 Π u1 (|Σ| = 0), and 1 5 Π u1 (|Σ| = 2) states to the predissociation line width of the 1 3 Σ u - -X 3 Σ g1 - transition, the broading and other predissociation features of the 1 3 Σ u - state are analyzed. From our calculations, it follows that the strong coupling between the bound 1 3 Σ u - state and the repulsive 1 5 Π u state causes the predissociation of the 1 3 Σ u - state at the vibrational levels v ' ≥ 8. In addition, our results suggest that the previously observed bands of Sn 2 in the visible range of 19000-20000 cm -1 should be reassigned into the mixing transitions among the X 3 Σ g,1 - -2 3 Σ u,0 - + and X 3 Σ g,0 + - -2 3 Σ u,1 + manifold. The results are expected to provide new comprehensive information for better understanding the spectra and dynamics of the electronic excited states of the Sn 2 molecule.