Theoretical Study of Spectral Properties of Boron Hydride Based on ab Initio Calculation
Objective The ab initio calculation method is based on the basic principles of quantum mechanics.Its essence lies in its independence from experimental data or empirical parameters,relying instead on theoretical derivations and computations to directly probe into the electronic structure and associated properties of molecules.This approach is pivotal for gaining an in-depth understand-ing of molecular structures and properties.When the accuracy of the calculations is utmost,the multi-reference configuration interac-tion(MRCI)method is favored due to its unique advantage of specifically considering strong interactions between multiple reference states.This feature is crucial for accurately describing complex electronic structures in molecular systems.Method The spectroscopic properties of the BH molecule have been thoroughly investigated.To correct for size inconsistency and enhance the accuracy of the calculations,an initial approximation of the electronic wave function is made using the Hartree-Fock method,then optimized using the state-averaged fully active space self-consistent field method,followed by the application of the multi-reference group state interaction method combined with the Davidson correction.On this basis,the spectral param-eters of the electronic states are obtained by solving the one-dimensional radial Schrödinger equation for nuclear motion using the LEVEL program.The MOLPRO software package is employed to calculate the transition dipole moments of the A1Π-X1Σ+states.parameters such as the Franck-Condon factor and the Einstein A factor are obtained by fitting using the LEVEL program.Additionally,the radiative lifetimes between vibrational-rotational energy levels are calculated.Ultimately,candidate scheme for laser cooling of BH molecules are identified.Results and discussions The results provide the potential energy curves for the ten Ʌ-S states corresponding to the three dissocia-tion limits of the BH molecule,as well as the spectroscopic constants of the bound-electron states.Key parameters such as the transition dipole moments,Franck-Condon factors,vibrational branching ratios,and the radiative lifetimes of the A1Π-X1Σ+states are calculated.Based on these data,a scheme for laser cooling of the A1Π-X1Σ+lepton driven by the main laser at a wavelength of 432.48 nm is proposed.This establishes a theoretical foundation for a more accurate and efficient molecular laser cooling tech-nique that is expected to be realized in the future.Conclusion This study proposes a candidate scheme for laser cooling of BH molecules.Utilizing the multi-reference configuration inter-action method,a detailed investigation of the spectroscopic properties of BH molecules has been undertaken,leading to the derivation of their corresponding electronic energy level structures.This research provides theoretical support for the experimental realization of laser cooling of BH molecules.With further calculations,we expect to achieve higher precision and broader applications in the future.
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