Spectral characteristics of low excited state of strontium monobromide molecule

Abstract

The electronic structures and single point energy of 14 lowest electronic states of ⁸⁸Sr⁷⁹Br molecule are optimized by using the internal contraction multi-reference configuration interaction method and relativistic effective core pseudo-potential basis. Because ⁸⁸Sr⁷⁹Br molecule belongs to heavy element system, the single point energy must be corrected to obtain more accurate spectral parameters. Therefore, Davidson is introduced to correct the energy inconsistency, nuclear valence correlation is used to correct the electron correlation effect of inner shell and valence shell, and the relativistic scalar effect is corrected by calculating the third-order Douglas-Kroll-Hess Hamilton single electron integral. According to the single point energy calculated by the modified optimization, the potential energy curves, electric dipole moments, and transition dipole moments of 14 lowest electronic states are obtained. Using the latest LEVEL8.0 program to fit the modified potential energy curve, the spectral constants, molecular constants and vibration energy levels of 5 lowest bound states of ⁸⁸Sr⁷⁹Br molecule are given. In order to explain the changing trend of spectral constants of homologous compounds, the spectral parameters of each compound are compared and analyzed in this paper. At the same time, the vibration energy levels and molecular constants of ⁸⁸Sr⁸¹Br molecule are also fitted and calculated for analyzing the influence of isotopes. The comparative analysis shows that the results of ⁸⁸Sr⁷⁹Br molecule are in better agreement with the experimental values. Finally, the Franck-Condon factors are gained by fitting the optimized single point energy and transition dipole moment of ⁸⁸Sr⁷⁹Br molecule. The transition band with the largest factor and obvious diagonalization is selected by analyzing the Franck-Condon factor of each transition band, and whether it meets the conditions for selecting laser cooling molecular system is judged. The radiation lifetimes of the transitions from the lowest two excited states to the ground state are calculated by combining the transition dipole moment, Franck-Condon factor, single point energy and vibration energy level of each electronic state. The results of this paper are in good agreement with the experimental values, which shows that the method in this paper is reliable. These spectral characteristic parameters provide theoretical support for further experimental measurement and construction of molecular laser cooling scheme of ⁸⁸Sr⁷⁹Br molecule.