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

The ground and excited states of Sn2 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 Sn2 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 Σg,0+ + -X3 Σg,1(Ms=±1) - transition may be detected experimentally; the sub-bands (0, 0), (1, 0), and (2, 0) of the a 1 Δg,2 -X3 Σg,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 15 Πu0+ , 15 Πu1 (|Σ| = 0), and 15 Πu1 (|Σ| = 2) states to the predissociation line width of the 13 Σu - -X3 Σg1 - transition, the broading and other predissociation features of the 13 Σu - state are analyzed. From our calculations, it follows that the strong coupling between the bound 13 Σu - state and the repulsive 15 Πu state causes the predissociation of the 13 Σu - state at the vibrational levels v ' ≥ 8. In addition, our results suggest that the previously observed bands of Sn2 in the visible range of 19000-20000 cm-1 should be reassigned into the mixing transitions among the X3 Σg,1 - -23 Σu,0- + and X3 Σg,0+ - -23 Σu,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 Sn2 molecule.