Accurate Computations On Electronic Structures Of Two Diatomic Molecules

The precise electronic structure and spectrum of the molecular system reflect the internal material structure information of the molecules.And we can analyse information such as the energy level structure,physical and chemical properties of the molecule from electronic structure and spectrum.However,experimental structural and spectral information of molecular systems is limited by the development of experimental techniques.The using of molecular orbital theory based on quantum mechanical ab initio calculations has become an important pathway to understand molecular electronic structures and spectrum.In this work,the highly accurate multi-reference configuration interaction method is used to study the electronic excited states of GeH⁺molecular ions and HF molecules,which both have been"controversial"in the previous reports,and obtain more accurate and comprehensive electronic information of these molecular systems.We recalculate the electronic structure of GeH⁺radical cation,in which the two lower dissociation limits were neglected in the previous study,and calculate the?-S states corresponding to the lowest four correct dissociation limits and the?states after considering the spin-orbit coupling effect.Some electronic excited states of the molecule are re-identified,and the perturbation and predissociation phenomenon caused by the increase of the electronic state density of the molecular system in the energy region of 47000-82000 cm^-1 are further explored.Then,recalculation is performed for the three Rydberg states of the HF molecule whose energy level order in previous computational studies was disputed.The Gaussian basis sets are calibrated and selected by atomic energy levels calculation,and then the electronic structure of the molecular Rydberg states is described more accurately.We obtain more accurate spectral information such as potential energy curves and spectroscopic constants.This thesis also studies the 19?-S states corresponding to the three dissociation limits of an alkali metal sulfide NaS molecule synthesized in the laboratory and which possibly exists in celestial bodies.And the electron correlation and spin-orbit coupling effects are considered in the calculation.The influence of these effects on the potential energy curves and spectroscopic constants of the system is discussed,and the spontaneous emission lifetimes between the spin-allowed electronic states are obtained.The above computational results of molecular structure and spectrum are of great significance in the fields of celestial body,atomic and molecular physics.